Carbon Sequestration Methods and Systems

ABSTRACT

Methods of sequestering carbon dioxide (CO 2 ) are provided. Aspects of the methods include contacting a CO 2  containing gaseous stream with an aqueous medium under conditions sufficient to produce a bicarbonate rich product. The resultant bicarbonate rich product (or a component thereof) is then combined with a cation source under conditions sufficient to produce a solid carbonate composition and product CO 2  gas, followed by injection of the product CO 2  gas into a subsurface geological location to sequester CO 2 . Also provided are systems configured for carrying out the methods.

CROSS-REFERENCE TO RELATED APPLICATION

This application is division of U.S. patent application Ser. No.14/861,996 filed on Sep. 22, 2015, now issued as U.S. Pat. No.10,197,747, which application, pursuant to 35 U.S.C. § 119(e), claimspriority to the filing date of U.S. Provisional Application Ser. No.62/054,322 filed on Sep. 23, 2014; the disclosure of which applicationsare herein incorporated by reference.

INTRODUCTION

Carbon dioxide (CO₂) is a naturally occurring chemical compound that ispresent in Earth's atmosphere as a gas. Sources of atmospheric CO₂ arevaried, and include humans and other living organisms that produce CO₂in the process of respiration, as well as other naturally occurringsources, such as volcanoes, hot springs, and geysers.

Additional major sources of atmospheric CO₂ include industrial plants.Many types of industrial plants (including cement plants, refineries,steel mills and power plants) combust various carbon-based fuels, suchas fossil fuels and syngases. Fossil fuels that are employed includecoal, natural gas, oil, petroleum coke and biofuels. Fuels are alsoderived from tar sands, oil shale, coal liquids, and coal gasificationand biofuels that are made via syngas.

The environmental effects of CO₂ are of significant interest. CO₂ iscommonly viewed as a greenhouse gas. Because human activities since theindustrial revolution have rapidly increased concentrations ofatmospheric CO₂, anthropogenic CO₂ has been implicated in global warmingand climate change, as well as increasing oceanic bicarbonateconcentration. Ocean uptake of fossil fuel CO₂ is now proceeding atabout 1 million metric tons of CO₂ per hour.

Concerns over anthropogenic climate change and ocean acidification,compounded with recent changes in U.S. Federal policy to include carbondioxide (CO₂) as a regulated air pollutant, have fueled an urgency todiscover scalable, cost effective, methods of carbon capture andsequestration (CCS). Typically, methods of CCS separate pure CO₂ fromcomplex flue streams, compress the purified CO₂, and finally inject itinto underground saline reservoirs for geologic sequestration. Thesemultiple steps are very energy and capital intensive.

SUMMARY

Methods of sequestering carbon dioxide (CO₂) are provided. Aspects ofthe methods include contacting a CO₂ containing gaseous stream with anaqueous medium under conditions sufficient to produce a bicarbonate richproduct. The resultant bicarbonate rich product (or a component thereof)is then combined with a cation source under conditions sufficient toproduce a solid carbonate composition and product CO₂ gas, followed byinjection of the product CO₂ gas into a subsurface geological locationto sequester CO₂. Also provided are systems configured for carrying outthe methods.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Size distribution of LCP droplets in various solutions at 25°C., as determined by nanoparticle tracking analysis (NTA). NTA ispreferred over dynamic light scattering in characterizing the particlesize distribution of LCP due to its sensitivity to dilute concentrationsand its spatial resolution, and has proven successful in detecting LCPin the past. These data suggest that LCP is a common, ubiquitous phasethat is expected to affect carbonate chemistry in many differentCO₂-containing aqueous systems and does not require the presence of Ca²⁺and/or Mg²⁺. (A) Simulated Cretaceous seawater at roughly seven timesatmospheric P_(CO2); measured DIC=1.8 mM carbon. In the geologic record,Earth's most significant and abundant carbonate rock formations arelimestones resulting from calcium carbonate biomineralization producedby calcifying marine taxa which were prolific during this Period, whenatmospheric carbon dioxide concentration was significantly higher (16).(B) Sand-filtered, modern seawater from Monterey Bay, Calif.; measuredDIC=1.7 mM carbon. (C) Simple synthetic LCP-containing solutionconsisting of 100 mM NaHCO₃ and 100 mM NaCl (D) Fetal Bovine Serum,1/100 diluted in deionized water and filtered through a 200 nm syringefilter; measured DIC=0.5 mM carbon. (Insets) Size distributions of thedetected scattering events (LCP droplets) in the respective data set.

FIG. 2. Results from nuclear magnetic resonance and nanoparticletracking analysis indicate that the bicarbonate-rich LCP behaves as atwo-phase, solution-state system. (A) ¹³C NMR data of a 100 mM NaHCO₃(100% ¹³C-enriched), 100 mM NaCl solution. The shoulder at 158.22 ppm isattributed to the presence of LCP, which has a composition similar to,but not identical to that of the mother solution. The small differencein chemical shift may be due to differences in pH between the LCP andmother solution. To ensure that the electrolyte behavior isun-adulterated, no chemical shift standard was added to the solution.(B) Deconvolution of the overlapping peaks in the ¹³C NMR spectrum in(A) suggests that approximately 30% of the inorganic carbon hasparticipated in LCP over 6.35 seconds (acquisition time) and 70% hasnot, remaining in the mother liquor phase for the duration. The T₂relaxation of the peaks was obtained through a CPMG-NMR method anddetermined to be 1.0 and 2.2 for the LCP and mother liquor phase,respectively, values that are consistent with solution states ofsolvated ions. The lower T₂ value for the LCP is consistent with the LCPbeing a more concentrated, viscous solution relative to the mothersolution. (C) The plot shows relative light scattering intensities ofdifferent sized species in solution; larger data points representimproved statistical certainty due to longer Brownian motion monitoring.SiO₂ nanoparticles were used as a calibration standard and the displayedcurve effectively modeled the refractive index of the small amount ofthem that were added to the reaction (red line, RI=1.51, shaded redarea). The statistically relevant (large, green shaded) data points inthe suspected LCP regime were modeled (dark green line, RI=1.355) and alower-limit fit of scattering intensities of LCP droplets (black line,RI=1.347) were modeled as well. The range of R.I. values for the LCPdroplets are consistent with saltwater solutions because they are only afew hundredths larger than that of fresh water alone. (D) The linearrelationship between saltwater salinity (g/L) and the RI is shown and istaken from literature (23). According to the relationship, LCP in thissolution has a lower-limit salinity of approximately 20 g/L but could beas high as approximately 60 g/L or more which is much more concentratedthan the mother solution from which they are derived.

FIG. 3. Bicarbonate-rich LCP displays a droplet moiety allowing it to befiltered and manipulated. (A) Using a nanofiltration membrane, overallDIC (bicarbonate) is concentrated along with bicarbonate-rich LCP in aninitial solution of 50 mM NaHCO₃ and 50 mM KCl in a way that is unusualfor small, monovalent ions suggesting that the bicarbonate ion isexisting in a larger moiety, such as the bicarbonate-rich LCP. (B)Nanoparticle tracking analysis (NTA) scattering stillshots demonstratethe concentration of bicarbonate-rich LCP. (C) Rejection (concentration)of sodium bicarbonate (NaHCO₃) using current membrane technologiesallowing for manipulation and concentration of the CO₂-derivedbicarbonate-rich LCP. The sudden drop in ion rejection of bicarbonatesuggests that the LCP droplet moiety has a size larger than 10 nm andbegins to pass through the membrane. Three types of membranes: reverseosmosis (RO 0.1-1 nm pore size, MWCO ˜0), nanofiltration (NF 1-10 nmpore size, MWCO <1000) and ultrafiltration (UF 10-100 nm pore size,MWCO >1000), where used to concentrate the same solution used in part A.Large rejections were seen until a membrane with pore sizes larger the10 nm were used, after which the bicarbonate moieties begin to passthrough the membrane; this is consistent with the magnitude of sizepredicted by the NTA. (D) The overall ionic strength of permeatesolutions passed through each of the various membranes verifies thesudden passage of bicarbonate ions once the pore diameter becomes largerthan the bicarbonate-rich LCP.

FIG. 4. CaCO₃ materials made through the reaction shown in equation (1)demonstrate desirable material mechanical properties and high solarreflectance. (A) Compressive strength data at 1-, 3-, 7-, 14- and28-days for three different mortar cube formulations: Ordinary portlandcement or OPC, (no OPC replacement), 15% IG and 15% IG-LCP, whereIG=interground limestone, LCP=liquid. The addition of IG limestonesimilar to what is produced through reaction (1) and a combination of IGand bicarbonate-rich LCP lead to early cure times and strengths that aresuperior to the currently used ordinary mix design. (B) Life cycleanalyses of different concrete formulations where traditional componentsare replaced by novel carbon-reducing components. The formulations arebased on a generic “moderate-strength” mix design. As Portland cement isreplaced by synthetic limestone produced from sequestered CO₂ via thereaction in equation (1), the carbon footprint of concrete dropssignificantly, even going negative as the concrete becomes a CO₂sequestering sink. (C) Life cycle analyses of mortar specimens in FIG.4A, where 15% OPC was replaced by quarried limestone and water wasreplaced by LCP liquid that contained 1% CO₂ by weight. Even a modestamount of limestone replacement to mortar formulations utilizingbicarbonate-rich LCP solutions results in a significant reduction of thecarbon footprint while improving cure time. (D) Solar reflectance (SR)spectra comparing Blue Planet synthetic CaCO₃ (blue line), technicalgrade TiO₂ (yellow line), Acmaea mitra mollusk shell (red line), Caleralimestone (black line) and GAF Quickstart roofing material (green line).The CaCO₃ material precipitated via the reaction in equation (1)displays superior albedo properties, having high solar reflectanceacross the entire solar spectrum, a property with significantimplications with regard to energy efficiency in cool materials.

FIG. 5. The Mg/Ca ratio affects bicarbonate-rich liquid condensed phasedroplets. The effect of changing [Mg²⁺]:[Ca²⁺] ratio to the formation ofbicarbonate-rich liquid condensed phase (LCP) droplets was measured bymeans of nanoparticle tracking analysis (NTA) in solutions containing0.2 mM divalent ions and 50 mM sodium bicarbonate. (A, C, E, G) Astill-shot of the scattering projection of solutions containing[Mg²⁺]:[Ca²⁺] ratios of 1:1, 2.5:1, 5:1, and 7:1, respectively. (B, D,F, and H) The size histograms of the LCP droplets obtained by NTA for A,C, E, and G, respectively. (I) The LCP droplet count as detected by thenanoparticle tracking analyzer vs. the [Mg²⁺]:[Ca²⁺] ratio in solution.The data was collected in triplicate and averaged with a standarddeviation of error in either direction. We see that the presence ofdivalent ions seems to promote the formation of large, robust anddetectable LCP as compared to solutions containing only monovalent ions(see FIG. 1C). The size distribution of the droplets are very similarfor all cases, however the amount of LCP droplets seems to changedepending on the [Mg²⁺]:[Ca²⁺] ratio as shown in I. At solutions near1:1 ratio (similar to Cretaceous seawater), there are many droplets, butas the solution increases in [Mg²⁺]:[Ca²⁺] ratio, the amount of dropletsdrops suddenly and then increases until, at a [Mg²⁺]:[Ca²⁺] ratio of 7:1(similar to modern seawater). This effect on the LCP by [Mg²⁺]:[Ca²⁺]may have a role in describing ocean acidification, explaining theextreme calcium carbonate deposition during the Cretaceous era, and evenexplaining why calcite forms near 1:1 ratios, but aragonite forms athigher ratios (5:1 and 7:1, shown on the plot in FIG. S1I).

FIG. 6. Bicarbonate ions form bicarbonate-rich liquid condensed phase.Still-shots of the scattering projections obtained by nanoparticletracking analysis (NTA) strongly suggest that the bicarbonate ionparticipates in a condensation, as reported for bicarbonate-rich LCP. A)A solution containing 100 mM NaHCO3 and 100 mM NaCl contain manyscattering events presumably due to the formation of bicarbonate-richLCP. B) A solution containing 200 mM NaCl does not display scatteringevents at the same conditions. This is evidence that the bicarbonate ionparticipates in a condensation to form bicarbonate-rich LCP even inrelatively simple, undersaturated solutions. The species seen in A are adistribution of sizes centered around 50-60 nm in diameter as shown inFIG. 1C of the main report.

FIG. 7. The standardization of nanoparticle tracking analysis withsilica particles for refractive index measurements. Scattering intensityvs. diameter of silica nanoparticles in water obtained from the NS500nanoparticle tracking analyzer. To establish a standard curve andcalibrate the NS500 NTA for refractive indices measurements, silica(SiO₂) nanoparticles (nanoComposix) of 50, and 80 nm (hydrated diametersof 62, and 92 nm, respectively) were used as the standard referencematerial (RI=1.51). A curve was fitted using the Raleigh approximation(equation S1) to fit the intensity of the scattering events with themeasured size of the particles. The area of the data points (bluecircles) represent the relative statistical certainty of themeasurement.

FIG. 8. Two pathways to calcium carbonate formation; a high pH pathwayand a low pH pathway. 0.25 M CaCl₂ was added to equal volumes of either0.5 M NaHCO₃ or 0.5 M Na₂CO₃ in a dump reaction manner and were analyzedimmediately post mixing. The results suggest that there are two distinctpathways toward calcium carbonate formation; a familiar one designatedin the main text as reaction 2 (CaCl₂ (aq) and Na₂CO₃ (aq) at high pH,carbonate pathway) and another pathway designated in the main text asreaction 1 (CaCl₂ (aq) into NaHCO₃ (aq) at neutral pH, bicarbonatepathway). (A) A Time Resolved Fourier Transform Infrared Spectra (FTIR)of a reaction 1 dump reaction at times of 0 seconds (purple), 10 seconds(green), 30 seconds (red), 30 minutes (blue) post mixing. Calciteinfrared active bond vibrational modes of, v3 (1400 cm−1), v1 (1087cm−1), v2 (877 cm−1), and v4 (714 cm−1) are seen. The asymmetrical C—Ostretching of the carbonate bond, v3, is seen shifting through abidentate, resulting in a characteristic calcite peak suggesting thatcalcium carbonate formation may be forming through a bicarbonate pathwaysimilar to one proposed in nature (I. Zondervan, R. E. Zeebe, B. Rost,U. Riebesell, Decreasing marine biogenic calcification: A negativefeedback on rising atmospheric pCO2. Global Biogeochemical Cycles 15,507 (2001)). The symmetric carbonate vibrational mode, v1, relates tofree carbonate available in the structure. Out of plane bending, v2, andin plane bending, v4, are identified by (877 cm−1) and (714 cm−1)respectively. (B) A FTIR spectra identifying CaCO₃ (calcite) formed byLCP Reaction 1, and Reaction 2. The end product of both pathways appearsto be identical. (C) A nanoparticle tracking analysis (NTA) still-shotimage of 0.25M NaHCO₃. Bicarbonate-rich liquid condensed phase dropletscan be seen. (D) A NTA still-shot image of a reaction 1 immediately postmixing provides a visualization of what is measured in time-resolvefashion in part A. (E) The chemical pathway of LCP-driven low pHreaction (Reaction 1) vs. conventional high pH reaction (Reaction 2),(F) The measured yields of reaction 1 vs. reaction 2, with respect toCaCO₃ and CO₂, as determined by DIC analysis. The results reinforce thedifference between reaction 1 and reaction 2 pathways due to differencesin evolved CO2 (expected for reaction 1). (G) The time-resolved pHresponse of reaction 1 dump reaction shows an initial drop in pH,presumably due to removal of bicarbonate. (H) The time-resolved pHresponse of reaction 2 dump reaction shows little pH drop suggestingthat carbonates are being consumed during mineral formation and arebuffered by bicarbonates. During the reaction of carbonate formation,liquid condensed phases (LCP) evolve in the presence of calcium ion andnucleating to form CaCO₃. As CaCO₃ precipitation proceeds, dehydrationof the reaction product occurs as seen by the drop of δ O—H vibrationalpeak. According to FTIR spectra in FIG. S5A, the structures wereinitially hydrated and amorphous as reported previously, showing broadpeaks in the observed range (K. Naka, Y. Tanaka, Y. Chujo, Effect ofAnionic Starburst Dendrimers on the Crystallization of CaCO3 in AqueousSolution: Size Control of Spherical Vaterite Particles. Langmuir 18,3655 (2002); L. Addadi, S. Raz, S. Weiner, Taking advantage of disorder:amorphous calcium carbonate and its roles in biomineralization. Adv.Mater. 15, 959 (2003)). As the reaction progresses, however, gradualappearance of sharp peaks are related to the development of crystallinestructure of the carbonate polymorphs as seen with the increase of 1400cm⁻¹ (v₃ asymmetrical CO₃), 1087 cm⁻¹ (v₁ symmetrical CO₃), 877 cm⁻¹ (v₂out-of-plane band of CO₃), and 714 cm⁻¹ (v₄ in-plane-band of CO₃) (J. D.Rodriguez-Blanco, S. Shaw, L. G. Benning, The kinetics and mechanisms ofamorphous calcium carbonate (ACC) crystallization to calcite, viavaterite. Nanoscale 3, 265 (2011)), indicating the formation of calcitephase (E. Loste, R. M. Wilson, R. Seshadri, F. C. Meldrum, The role ofmagnesium in stabilising amorphous calcium carbonate and controllingcalcite morphologies. Journal of Crystal Growth 254, 206 (2003)). Thisparticular reaction was denoted as Reaction 1 in the main report and wascompared to conventional CaCO₃ precipitation pathway, Reaction 2.

CaCl₂(aq)+2NaHCO₃(aq)↔CaCO₃(s)+2NaCl(aq)+H₂O(I)+CO₂(g)  Reaction 1:

CaCl₂(aq)+Na₂CO₃(aq)↔CaCO₃(s)+2NaCl(aq)  Reaction 2:

The products as the result of Reaction 1 and 2 are identical as shown inFIG. S5B. The yield of CO₂ and CaCO₃ were 90% and 80%, respectively,confirming the stoichiometry and chemical pathway of Reaction 1. pH wasalso measured in a time-resolved fashion and suggests that reaction 1occurs at a lower pH compared to the conventional Reaction 2. This isdirectly related to LCP-formation mechanism as Ca²⁺ has the propensityto interact with HCO₃ ⁻, enabling precipitation reaction to take placeat neutral pH. In both cases, pHs in the initial stages decreaseslightly due to onset of CaCO₃ precipitation.

FIG. 9. Illustration depicting how the two-phase bicarbonate-rich LCPsystem might alter the interpretation of system measurements such as pH.(A) Hypothetical one-phase system, at relatively neutral pH, thatconsists of HCO₃ ⁻ and CO₃ ²⁻ ions charge balanced with H⁺ and variousM^(n+) cations, e.g., Na⁺, K⁺, Ca²⁺, etc. (B) A system containing thesame constituents as (A) but now they are arranged in a two-phase systemthat has bicarbonate-rich LCP, illustrated by the single large droplet.Even though the systems are identical in a global sense (overall DIC andalkalinity), the variables measured only in the bulk of the two-phasesystem, such as pH, conductivity, and selected ion concentrations, willnot reflect the contents of the LCP. This can lead to misinterpretationof the system behavior unless the two-phase system is considered. Forthis illustration, the pH of the two-phase system would be higher due tothe known sequestration of H⁺ in the LCP, leading to the falseconclusion that the overall HCO₃ ⁻/CO₃ ²⁻ ratio has dropped when, in aglobal sense, it has remained constant. In a two-phase system, such asone containing bicarbonate-rich LCP, pH and alkalinity are independentdue to the presence of an extra degree of freedom.

FIG. 10. An illustration of a two phase system that can alter theinterpretation of system measurements such as pH. On the left is ahypothetical one phase system which shows speciation ideally to yield a1:10 carbonate to bicarbonate ratio. The system on the right containsthe same constituents as on the left but it is arranged in a two-phasesystem containing bicarbonate-rich liquid condensed phase dropletswithin a mother liquor which is at a carbonate-to-bicarbonate ratio of1:5. Even though the systems are identical in a global sense, themeasured pH value is different between the systems which would lead toincorrect interpretations if the two-phase system is not considered.

FIG. 11. The concentration of bicarbonate-rich liquid LCP droplets (asmeasured by nanoparticle tracking analysis) qualitatively matches theactivity drop of ions predicted from our thermodynamic analysis. (A)Pitzer equations model bicarbonate solutions empirically which considersall of the known contributions to activity loss. Debye-Huckel, modelsonly consider columbic interactions. By subtracting the activitiespredicted by Pizter Equations from those predicted by D-H theory, weisolate the activity loss of ions due to bicarbonate-rich LCP. Ionpairing and prenucleation clustering is negligible due to the neutralpH, lack of divalent ions, and the weak ion associations known for allthree ions (Na⁺, Cl⁻, HCO₃ ⁻). (B) The difference in ion activitybetween actual ion activities (approximated using Pitzer's equations)and that predicted by Debye-Hückel theory for a 50 mM NaHCO₃ withvarying amounts of HCl added to adjust pH. Species with positivedeviations (lower activities) are interpreted as strong candidates to beparticipating in the LCP phase. Negative deviations are interpreted tobe species that are relatively enriched in the bulk phase and areexcluded from the LCP. The composition of the LCP phase is then the sumof the positive deviations of the curves, which provides the amounts ofspecies missing from bulk solution (C) The comparison of measured LCPdroplet concentrations via NTA vs. the predicted percent of ionsparticipating in LCP as predicted from part B. The NTA experimental datawas collected in triplicate and is presented as an average with astandard deviation of error in either direction. The amount of LCPdroplets detected by NTA decreases in a way qualitatively similar to ourprediction. The drop in concentration of LCP droplets detected occursmore rapidly than the drop according to the Pitzer equations. Thissuggests that the LCP droplets may be smaller as well as fewer as the pHis lowered and therefore are not being detected by the NTA (which has asize detection lower limit of 40 nm). We speculate that there may be aspinodal for the LCP below pH 7.5. This would be consistent with an LCPphase that is bicarbonate-rich and slightly acidic as reportedpreviously as the energy of interfacial formation would be reduced inthis environment.

FIG. 12. A flow process diagram illustrating the proposed carbonsequestration mechanism allowed by the discovery of bicarbonate-richLCP. The four stages of the process are: (I) Pre-Capture: the creationof the CO₂ capture solution, (II) Capture: the capture solution iscontacted with flue gas, (III) Concentrate: dilute solutions of LCP areconcentrated by membrane dewatering, and (IV) Precipitate: a hard watersource is combined with the concentrated LCP solution to precipitatesynthetic limestone (calcium carbonate, CaCO₃).

FIG. 13. Models for the LCP Technology in place at a 500 MW power plant.(A) Coal-fired power plant. (B) Natural gas-fired power plant. Each caseassumes the solution developed at the Pre-Capture stage will have 200mmol alkalinity available to capture CO₂, and that the CaCO₃precipitation occurs by reaction of one equivalent of Ca²⁺ with twoequivalents of HCO₃ ⁻.

DETAILED DESCRIPTION

Methods of sequestering carbon dioxide (CO₂) are provided. Aspects ofthe methods include contacting a CO₂ containing gaseous stream with anaqueous medium under conditions sufficient to produce a bicarbonate richproduct. The resultant bicarbonate rich product (or a component thereof)is then combined with a cation source under conditions sufficient toproduce a solid carbonate composition and product CO₂ gas, followed byinjection of the product CO₂ gas into a subsurface geological locationto sequester CO₂. Also provided are systems configured for carrying outthe methods.

Before the present invention is described in greater detail, it is to beunderstood that this invention is not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present invention will be limited only by the appendedclaims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Certain ranges are presented herein with numerical values being precededby the term “about.” The term “about” is used herein to provide literalsupport for the exact number that it precedes, as well as a number thatis near to or approximately the number that the term precedes. Indetermining whether a number is near to or approximately a specificallyrecited number, the near or approximating un-recited number may be anumber which, in the context in which it is presented, provides thesubstantial equivalent of the specifically recited number.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present invention, representativeillustrative methods and materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present invention is not entitled to antedate suchpublication by virtue of prior invention. Further, the dates ofpublication provided may be different from the actual publication dateswhich may need to be independently confirmed.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinvention. Any recited method can be carried out in the order of eventsrecited or in any other order which is logically possible.

Methods

As summarized above, aspects of the invention include CO₂ sequestrationprocesses, i.e., processes (methods, protocols, etc.) that result in CO₂sequestration. By “CO₂ sequestration” is meant the removal orsegregation of an amount of CO₂ from an environment, such as the Earth'satmosphere or a gaseous waste stream produced by an industrial plant, sothat some or all of the CO₂ is no longer present in the environment fromwhich it has been removed. CO₂ sequestering methods of the inventionsequester CO₂ by producing a substantially pure subsurface injectableCO2 product gas and a storage stable carbon dioxide sequestering productfrom an amount of CO₂, such that the CO₂ is sequestered. The storagestable CO₂ sequestering product is a storage stable composition thatincorporates an amount of CO₂ into a storage stable form, such as anabove-ground storage or underwater storage stable form, so that the CO₂is no longer present as, or available to be, a gas in the atmosphere.Sequestering of CO₂ according to methods of the invention results inprevention of CO₂ gas from entering the atmosphere and allows forlong-term storage of CO₂ in a manner such that CO₂ does not become partof the atmosphere.

Aspects of such protocols include contacting a CO₂ containing gas withan aqueous medium to remove CO₂ from the CO₂ containing gas. The CO₂containing gas may be pure CO₂ or be combined with one or more othergasses and/or particulate components, depending upon the source, e.g.,it may be a multi-component gas (i.e., a multi-component gaseousstream). In certain embodiments, the CO₂ containing gas is obtained froman industrial plant, e.g., where the CO₂ containing gas is a waste feedfrom an industrial plant. Industrial plants from which the CO₂containing gas may be obtained, e.g., as a waste feed from theindustrial plant, may vary. Industrial plants of interest include, butare not limited to, power plants and industrial product manufacturingplants, such as but not limited to chemical and mechanical processingplants, refineries, cement plants, steel plants, etc., as well as otherindustrial plants that produce CO₂ as a byproduct of fuel combustion orother processing step (such as calcination by a cement plant). Wastefeeds of interest include gaseous streams that are produced by anindustrial plant, for example as a secondary or incidental product, of aprocess carried out by the industrial plant.

Of interest in certain embodiments are waste streams produced byindustrial plants that combust fossil fuels, e.g., coal, oil, naturalgas, as well as man-made fuel products of naturally occurring organicfuel deposits, such as but not limited to tar sands, heavy oil, oilshale, etc. In certain embodiments, power plants are pulverized coalpower plants, supercritical coal power plants, mass burn coal powerplants, fluidized bed coal power plants, gas or oil-fired boiler andsteam turbine power plants, gas or oil-fired boiler simple cycle gasturbine power plants, and gas or oil-fired boiler combined cycle gasturbine power plants. Of interest in certain embodiments are wastestreams produced by power plants that combust syngas, i.e., gas that isproduced by the gasification of organic matter, e.g., coal, biomass,etc., where in certain embodiments such plants are integratedgasification combined cycle (IGCC) plants. Of interest in certainembodiments are waste streams produced by Heat Recovery Steam Generator(HRSG) plants. Waste streams of interest also include waste streamsproduced by cement plants. Cement plants whose waste streams may beemployed in methods of the invention include both wet process and dryprocess plants, which plants may employ shaft kilns or rotary kilns, andmay include pre-calciners. Each of these types of industrial plants mayburn a single fuel, or may burn two or more fuels sequentially orsimultaneously. A waste stream of interest is industrial plant exhaustgas, e.g., a flue gas. By “flue gas” is meant a gas that is obtainedfrom the products of combustion from burning a fossil or biomass fuelthat are then directed to the smokestack, also known as the flue of anindustrial plant.

Waste streams produced by cement plants are also suitable for systemsand methods of the invention. Cement plant waste streams include wastestreams from both wet process and dry process plants, which plants mayemploy shaft kilns or rotary kilns, and may include pre-calciners. Theseindustrial plants may each burn a single fuel, or may burn two or morefuels sequentially or simultaneously. Other industrial plants such assmelters and refineries are also useful sources of waste streams thatinclude carbon dioxide.

Industrial waste gas streams may contain carbon dioxide as the primarynon-air derived component, or may, especially in the case of coal-firedpower plants, contain additional components (which may be collectivelyreferred to as non-CO₂ pollutants) such as nitrogen oxides (NOx), sulfuroxides (SOx), and one or more additional gases. Additional gases andother components may include CO, mercury and other heavy metals, anddust particles (e.g., from calcining and combustion processes).Additional non-CO₂ pollutant components in the gas stream may alsoinclude halides such as hydrogen chloride and hydrogen fluoride;particulate matter such as fly ash, dusts, and metals including arsenic,beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead,manganese, mercury, molybdenum, selenium, strontium, thallium, andvanadium; and organics such as hydrocarbons, dioxins, and PAH compounds.Suitable gaseous waste streams that may be treated have, in someembodiments, CO₂ present in amounts of 200 ppm to 1,000,000 ppm; or 200ppm to 500,000 ppm; or 200 ppm to 100,000 ppm; or 200 ppm to 10,000; or200 ppm to 5,000 ppm; or 200 ppm to 2000 ppm; or 200 ppm to 1000 ppm; or200 to 500 ppm; or 500 ppm to 1,000,000 ppm; or 500 ppm to 500,000 ppm;or 500 ppm to 100,000 ppm; or 500 ppm to 10,000; or 500 ppm to 5,000ppm; or 500 ppm to 2000 ppm; or 500 ppm to 1000 ppm; or 1000 ppm to1,000,000 ppm; or 1000 ppm to 500,000 ppm; or 1000 ppm to 100,000 ppm;or 1000 ppm to 10,000; or 1000 ppm to 5,000 ppm; or 1000 ppm to 2000ppm; or 2000 ppm to 1,000,000 ppm; or 2000 ppm to 500,000 ppm; or 2000ppm to 100,000 ppm; or 2000 ppm to 10,000; or 2000 ppm to 5,000 ppm; or2000 ppm to 3000 ppm; or 5000 ppm to 1,000,000 ppm; or 5000 ppm to500,000 ppm; or 5000 ppm to 100,000 ppm; or 5000 ppm to 10,000; or10,000 ppm to 1,000,000 ppm; or 10.00 ppm to 500,000 ppm; or 10,000 ppmto 100,000 ppm; or 50,000 ppm to 1,000,000 ppm; or 50,000 ppm to 500,000ppm; or 50,000 ppm to 100,000 ppm; or 100,000 ppm to 1,000,000 ppm; or100,000 ppm to 500,000 ppm; or 200,000 ppm to 1000 ppm, including200,000 ppm to 2000 ppm, for example 180,000 ppm to 2000 ppm, or 180,000ppm to 5000 ppm, also including 180,000 ppm to 10,000 ppm.

The waste streams, particularly various waste streams of combustion gas,may include one or more additional non-CO₂ components, for example only,water, NOx (mononitrogen oxides: NO and NO₂), SOx (monosulfur oxides:SO, SO₂ and SO₃), VOC (volatile organic compounds), heavy metals suchas, but not limited to, mercury, and particulate matter (particles ofsolid or liquid suspended in a gas). Flue gas temperature may also vary.In some embodiments, the temperature of the flue gas comprising CO₂ isfrom 0° C. to 2000° C., or 0° C. to 1000° C., or 0. degree ° C. to 500°C., or 0° C. to 100° C., or 0° C. to 50° C., or 10° C. to 2000° C., or10° C. to 1000° C., or 10° C. to 500° C., or 10° C. to 100° C., or 10°C. to 50° C., or 50° C. to 2000° C., or 50° C. to 1000° C., or 50° C. to500° C., or 50° C. to 100° C., or 100° C. to 2000° C., or 100° C. to1000° C., or 100° C. to 500° C., or 500° C. to 2000° C., or 500° C. to1000° C., or 500° C. to 800° C., or such as from 60° C. to 700° C., andincluding 100° C. to 400° C.

In sequestering CO₂ from a CO₂-containing gas, a CO₂-containing gas maybe contacted with an aqueous medium under conditions sufficient toremove CO₂ from the CO₂-containing gas and produce a bicarbonatecomponent, which bicarbonate component may then be contacted with acation source to produce a substantially pure CO₂ product gas and acarbonate CO₂ sequestering component, e.g., as described in greaterdetail below.

The aqueous medium may vary, ranging from fresh water to bicarbonatebuffered aqueous media. Bicarbonate buffered aqueous media employed inembodiments of the invention include liquid media in which a bicarbonatebuffer is present. As such, liquid aqueous media of interest includedissolved CO₂, water, carbonic acid (H₂CO₃), bicarbonate ions (HCO₃ ⁻),protons (H⁺) and carbonate ions (CO₃ ²⁻). The constituents of thebicarbonate buffer in the aqueous media are governed by the equation:

CO₂+H₂O

H₂CO₃

H⁺+HCO₃ ⁻

2H⁺+CO₃ ²⁻

The pH of the bicarbonate buffered aqueous media may vary, ranging insome instances from 7 to 11, such as 8 to 11, e.g., 8 to 10, including 8to 9. In some instances, the pH ranges from 8.2 to 8.7, such as from 8.4to 8.55. The bicarbonate buffered aqueous medium may be a naturallyoccurring or man-made medium, as desired. Naturally occurringbicarbonate buffered aqueous media include, but are not limited to,waters obtained from seas, oceans, lakes, swamps, estuaries, lagoons,brines, alkaline lakes, inland seas, etc. Man-made sources ofbicarbonate buffered aqueous media may also vary, and may include brinesproduced by water desalination plants, and the like. Of interest in someinstances are waters that provide for excess alkalinity, which isdefined as alkalinity that is provided by sources other than bicarbonateion. In these instances, the amount of excess alkalinity may vary, solong as it is sufficient to provide 1.0 or slightly less, e.g., 0.9,equivalents of alkalinity. Waters of interest include those that provideexcess alkalinity (meq/liter) of 30 or higher, such as 40 or higher, 50or higher, 60 or higher, 70 or higher, 80 or higher, 90 or higher, 100or higher, etc. Where such waters are employed, no other source ofalkalinity, e.g., NaOH, is required.

In some instances, the aqueous medium that is contacted with the CO₂containing gas is one which, in addition to the bicarbonate bufferingsystem (e.g., as described above), further includes an amount ofdivalent cations. Inclusion of divalent cations in the aqueous mediumcan allow the concentration of bicarbonate ion in the bicarbonate richproduct to be increased, thereby allowing a much larger amount of CO₂ tobecome sequestered as bicarbonate ion in the bicarbonate rich product.In such instances, bicarbonate ion concentrations that exceed 5,000 ppmor greater, such as 10,000 ppm or greater, including 15,000 ppm orgreater may be achieved. For instance, calcium and magnesium occur inseawater at concentrations of 400 and 1200 ppm respectively. Through theformation of a bicarbonate rich product using seawater (or an analogouswater as the aqueous medium), bicarbonate ion concentrations that exceed10,000 ppm or greater may be achieved.

In such embodiments, the total amount of divalent cation source in themedium, which divalent cation source may be made up of a single divalentcation species (such as Ca²⁺) or two or more distinct divalent cationspecies (e.g., Ca²⁺, Mg²⁺, etc.), may vary, and in some instances is 100ppm or greater, such as 200 ppm or greater, including 300 ppm orgreater, such as 500 ppm or greater, including 750 ppm or greater, suchas 1,000 ppm or greater, e.g., 1,500 ppm or greater, including 2,000 ppmor greater. Divalent cations of interest that may be employed, eitheralone or in combination, as the divalent cation source include, but arenot limited to: Ca²⁺, Mg²⁺, Be²⁺, Ba²⁺, Sr²⁺, Pb²⁺, Fe²⁺, Hg²⁺ and thelike. Other cations of interest that may or may not be divalent include,but are not limited to: Na⁺, K⁺, NH⁴⁺, and Li⁺, as well as cationicspecies of Mn, Ni, Cu, Zn, Cu, Ce, La, Al, Y, Nd, Zr, Gd, Dy, Ti, Th, U,La, Sm, Pr, Co, Cr, Te, Bi, Ge, Ta, As, Nb, W, Mo, V, etc. Naturallyoccurring aqueous media which include a cation source, divalent orotherwise, and therefore may be employed in such embodiments include,but are not limited to: aqueous media obtained from seas, oceans,estuaries, lagoons, brines, alkaline lakes, inland seas, etc.

In some instances, the aqueous medium is one that has been subjected toan alkali recovery process, such as a membrane mediated alkali recoveryprocess. In such instances, prior to contact with the CO₂ containinggas, the aqueous medium is subjected to a process that results in anincrease in the pH of the aqueous medium. Of interest are membranemediated processes, such as forward osmosis mediated process. Alkalirecovery processes of interest include, but are not limited to, thosedescribed in PCT Application Serial No: PCT/US2015/018361 published asWO 2015/134408; the disclosure of which is herein incorporated byreference.

Contact of the CO₂ containing gas and bicarbonate buffered aqueousmedium is done under conditions sufficient to remove CO₂ from the CO₂containing gas (i.e., the CO₂ containing gaseous stream), and increasethe bicarbonate ion concentration of the buffered aqueous medium toproduce a bicarbonate rich product. The bicarbonate rich product is, insome instances, a two-phase liquid that includes droplets of a liquidcondensed phase (LCP) in a bulk liquid, e.g., bulk solution. By “liquidcondensed phase” or “LCP” is meant a phase of a liquid solution whichincludes bicarbonate ions wherein the concentration of bicarbonate ionsis higher in the LCP phase than in the surrounding, bulk liquid.

LCP droplets are characterized by the presence of a meta-stablebicarbonate-rich liquid precursor phase in which bicarbonate ionsassociate into condensed concentrations exceeding that of the bulksolution and are present in a non-crystalline solution state. The LCPcontains all of the components found in the bulk solution that isoutside of the interface. However, the concentration of the bicarbonateions is higher than in the bulk solution. In those situations where LCPdroplets are present, the LCP and bulk solution may each containion-pairs and pre-nucleation clusters (PNCs). When present, the ionsremain in their respective phases for long periods of time, as comparedto ion-pairs and PNCs in solution.

The bulk phase and LCP are characterized by having different K_(eq),different viscosities, and different solubilities between phases.Bicarbonate, carbonate, and divalent ion constituents of the LCPdroplets are those that, under appropriate conditions, may aggregateinto a post-critical nucleus, leading to nucleation of a solid phase andcontinued growth. While the association of bicarbonate ions withdivalent cations, e.g., Ca²⁺, in the LCP droplets may vary, in someinstances bidentate bicarbonate ion/divalent cation species may bepresent. For example, in LCPs of interest, Ca²⁺/bicarbonate ionbidentate species may be present. While the diameter of the LCP dropletsin the bulk phase of the LCP may vary, in some instances the dropletshave a diameter ranging from 1 to 500 nm, such as 10 to 100 nm. In theLCP, the bicarbonate to carbonate ion ratio, (i.e., the HCO₃ ⁻/CO₃ ²⁻ratio) may vary, and in some instances is 10 or greater to 1, such as 20or greater to 1, including 25 or greater to 1, e.g., 50 or greater to 1.Additional aspects of LCPs of interest are found in Bewernitz et al., “Ametastable liquid precursor phase of calcium carbonate and itsinteractions with polyaspartate,” Faraday Discussions. 7 Jun. 2012. DOI:10.1039/c2fd20080e (2012) 159: 291-312. The presence of LCPs may bedetermined using any convenient protocol, e.g., the protocols describedin Faatz et al., Advanced Materials, 2004, 16, 996-1000; Wolf et al.,Nanoscale, 2011, 3, 1158-1165; Rieger et al., Faraday Discussions, 2007,136, 265-277; and Bewernitz et al., Faraday Discussions, 2012, 159,291-312.

Where the bicarbonate rich product has two phases, e.g., as describedabove, the first phase may have a higher concentration of bicarbonateion than a second phase, where the magnitude of the difference inbicarbonate ion concentration may vary, ranging in some instances from0.1 to 4, such as 1 to 2. For example, in some embodiments, abicarbonate rich product may include a first phase in which thebicarbonate ion concentration ranges from 1000 ppm to 5000 ppm, and asecond phase where the bicarbonate ion concentration is higher, e.g.,where the concentration ranges from 5000 ppm to 6000 ppm or greater,e.g., 7000 ppm or greater, 8000 ppm or greater, 9000 ppm or greater,10,000 ppm or greater, 25,000 ppm or greater, 50,000 ppm or greater,75,000 ppm or greater, 100,000 ppm, 500,000 or greater.

In addition to the above characteristics, a given bicarbonate richproduct may include a number of additional markers which serve toidentify the source of CO₂ from it has been produced. For example, agiven bicarbonate component may include markers which identify the waterfrom which it has been produced. Waters of interest include naturallyoccurring waters, e.g., waters obtained from seas, oceans, lakes,swamps, estuaries, lagoons, brines, alkaline lakes, inland seas, as wellas man-made waters, e.g., brines produced by water desalination plants,and the like. In such instances, markers that may be present includeamounts of one or more of the following elements: Ca, Mg, Be, Ba, Sr,Pb, Fe, Hg, Na, K, Li, Mn, Ni, Cu, Zn, Cu, Ce, La, Al, Y, Nd, Zr, Gd,Dy, Ti, Th, U, La, Sm, Pr, Co, Cr, Te, Bi, Ge, Ta, As, Nb, W, Mo, V,etc. Alternatively or in addition to the above markers, a givenbicarbonate component may include markers which identify the particularCO₂-containing gas used to produce the bicarbonate component. Suchmarkers may include, but are not limited to, one or more of: nitrogen,mononitrogen oxides, e.g., NO, NO₂, and NO₃, oxygen, sulfur, monosulfuroxides, e.g., SO, SO₂ and SO₃), volatile organic compounds, e.g.,benzo(a)pyrene C₂0H₁₂, benzo(g,h,l)perylene C₂₂H₁₂,dibenzo(a,h)anthracene C₂₂H₁₄, etc. Particulate components that may bepresent in the CO₂ containing gas from which the bicarbonate componentis produced and therefore which may be present in the bicarbonatecomponent include, but are not limited to particles of solids or liquidssuspended in the gas, e.g., heavy metals such as strontium, barium,mercury, thallium, etc. When present, such markers may vary in theiramounts, ranging in some instances from 0.1 to 10,000, such as 1 to5,000 ppm. Of interest in certain embodiments are agents (referred toherein as “bicarbonate promoters” or “BLCP promoters”) that promote theproduction of high-bicarbonate-content bicarbonate additive (which mayalso be referred to herein as a bicarbonate admixture), e.g., bypromoting the production and/or stabilization of BLCPs, e.g.,facilitating the formation of a BLCP in a bicarbonate-containingsolution while preventing precipitation of the solution's components toform solid carbonate-containing materials. A high-bicarbonate-contentbicarbonate component is one that has a bicarbonate content of 0.1 wt. %or greater, such as 4 wt. % or greater, including 10 wt. % or greater,such as a bicarbonate component having a bicarbonate content rangingfrom 5 to 40 wt. %, such as 10 to 20 wt. %. The amount of bicarbonatepromoter present in a given bicarbonate component may vary, where insome instances the amount ranges from 0.000001 wt. % to 40 wt. %, suchas 0.0001 to 20 wt. % and including 0.001 to 10 wt. %. Such promotersare further described in U.S. patent application Ser. No. 14/112,495;the disclosure of which is herein incorporated by reference.

As indicated above, in sequestering CO₂ according to certain embodimentsof the invention, the CO₂ containing gas is contacted with an aqueousmedium under conditions sufficient to produce the bicarbonate-richproduct. The CO₂ containing gas may be contacted with the aqueous mediumusing any convenient protocol. For example, contact protocols ofinterest include, but are not limited to: direct contacting protocols,e.g., bubbling the gas through a volume of the aqueous medium,concurrent contacting protocols, i.e., contact between unidirectionallyflowing gaseous and liquid phase streams, countercurrent protocols,i.e., contact between oppositely flowing gaseous and liquid phasestreams, and the like. Contact may be accomplished through use ofinfusers, bubblers, fluidic Venturi reactors, spargers, gas filters,sprays, trays, or packed column reactors, and the like, as may beconvenient. The process may be a batch or continuous process.

Contact occurs under conditions such that a substantial portion of theCO₂ present in the CO₂ containing gas goes into solution to producebicarbonate ions. In some instances, 5% or more, such as 10% or more,including 20% or more of all the bicarbonate ions in the initialexpanded liquid phase solution (mother liquor) become sequestered inLCPs. Where desired, the CO₂ containing gas is contacted with thebicarbonate buffered aqueous medium in the presence of a catalyst (i.e.,an absorption catalyst) that mediates the conversion of CO₂ tobicarbonate. Catalysts of interest are further described in U.S. patentapplication Ser. No. 14/112,495; the disclosure of which is hereinincorporated by reference.

Where desired, following production of the LCP containing liquid, theresultant LCP containing liquid may be manipulated to increase theamount or concentration of LCP droplets in the liquid. As such,following production of the bicarbonate containing liquid, thebicarbonate containing liquid may be further manipulated to increase theconcentration of bicarbonate species and produce a concentratedbicarbonate liquid. In some instances, the bicarbonate containing liquidis manipulated in a manner sufficient to increase the pH. In suchinstances, the pH may be increased by an amount ranging from 0.1 to 6 pHunits, such as 1 to 3 pH units. The pH of the concentrated bicarbonateliquid of such as step may vary, ranging in some instances from 5.0 to13.0, such as 6.5 to 8.5. The concentration of bicarbonate species inthe concentrated bicarbonate liquid may vary, ranging in some instancesfrom 1 to 1000 mM, such as 20 to 200 mM and including 50 to 100 mM. Insome instances, the concentrated bicarbonate liquid may further includean amount of carbonate species. While the amount of carbonate speciesmay vary, in some instances the carbonate species is present in anamount ranging from 0.01 to 800 mM, such as 10 to 100 mM.

The pH of the bicarbonate liquid may be increased using any convenientprotocol. In some instances, an electrochemical protocol may be employedto increase the pH of the bicarbonate liquid to produce the concentratedbicarbonate liquid. Electrochemical protocols may vary, and in someinstances include those employing an ion exchange membrane andelectrodes, e.g., as described in U.S. Pat. Nos. 8,357,270; 7,993,511;7,875,163; and 7,790,012; the disclosures of which are hereinincorporated by reference. Alkalinity of the bicarbonate containingliquid may also be accomplished by adding a suitable amount of achemical agent to the bicarbonate containing liquid. Chemical agents foreffecting proton removal generally refer to synthetic chemical agentsthat are produced in large quantities and are commercially available.For example, chemical agents for removing protons include, but are notlimited to, hydroxides, organic bases, super bases, oxides, ammonia, andcarbonates. Hydroxides include chemical species that provide hydroxideanions in solution, including, for example, sodium hydroxide (NaOH),potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), or magnesiumhydroxide (Mg(OH)₂). Organic bases are carbon-containing molecules thatare generally nitrogenous bases including primary amines such as methylamine, secondary amines such as diisopropylamine, tertiary such asdiisopropylethylamine, aromatic amines such as aniline, heteroaromaticssuch as pyridine, imidazole, and benzimidazole, and various formsthereof. In some embodiments, an organic base selected from pyridine,methylamine, imidazole, benzimidazole, histidine, and a phophazene isused to remove protons from various species (e.g., carbonic acid,bicarbonate, hydronium, etc.) for precipitation of precipitationmaterial. In some embodiments, ammonia is used to raise pH to a levelsufficient to precipitate precipitation material from a solution ofdivalent cations and an industrial waste stream. Super bases suitablefor use as proton-removing agents include sodium ethoxide, sodium amide(NaNH₂), sodium hydride (NaH), butyl lithium, lithium diisopropylamide,lithium diethylamide, and lithium bis(trimethylsilyl)amide. Oxidesincluding, for example, calcium oxide (CaO), magnesium oxide (MgO),strontium oxide (SrO), beryllium oxide (BeO), and barium oxide (BaO) arealso suitable proton-removing agents that may be used.

Another type of further manipulation following production that may beemployed is a dewatering of the initial barcarbonate containing liquidto produce a concentrated bicarbonate containing liquid, e.g., aconcentrated LCP liquid. Dewatering may be accomplished using anyconvenient protocol, such as via contacting the LCP composition with asuitable membrane, such as an ultrafiltration membrane, to remove waterand certain species, e.g., NaCl, HCl, H₂CO₃ but retain LCP droplets,e.g., as described in greater detail in U.S. application Ser. No.14/112,495; the disclosure of which is herein incorporated by referenceFollowing preparation of the bicarbonate rich product (as well as anystorage thereof, as desired), the bicarbonate rich product or componentthereof (e.g., LCP) is manipulated to produce a CO₂ containing productgas and a solid phase carbonate composition. In certain instances ofsuch embodiments, the bicarbonate rich product or component thereof(e.g., LCP) is combined with a cation source (e.g., a source of one ormore alkaline earth metal cations) under conditions sufficient toproduce a solid carbonate composition. Cations of different valances canform solid carbonate compositions (e.g., in the form of carbonateminerals). In some instances, monovalent cations, such as sodium andpotassium cations, may be employed. In other instances, divalentcations, such as alkaline earth metal cations, e.g., calcium andmagnesium cations, may be employed. When cations are added to thebicarbonate rich product or component thereof (e.g., LCP), precipitationof carbonate solids, such as amorphous calcium carbonate when thedivalent cations include Ca²⁺, may be produced with a stoichiometricratio of one carbonate-species ion per cation.

Any convenient cation source may be employed in such instances. Cationsources of interest include, but are not limited to, the brine fromwater processing facilities such as sea water desalination plants,brackish water desalination plants, groundwater recovery facilities,wastewater facilities, and the like, which produce a concentrated streamof solution high in cation contents. Also of interest as cation sourcesare naturally occurring sources, such as but not limited to nativeseawater and geological brines, which may have varying cationconcentrations and may also provide a ready source of cations to triggerthe production of carbonate solids from the bicarbonate rich product orcomponent thereof (e.g., LCP). The cation source employed in such solidcarbonate production steps may be the same as or different from theaqueous media employed in the bicarbonate rich product production step,e.g., as described above. For example, the aqueous medium employed toproduce a bicarbonate rich product may be native seawater with a calciumcation concentration of approximately 400 ppm. A more concentratedcation solution, such as the brine concentrate from a seawaterdesalination plant, with over twice the native seawater concentration ofcalcium cation, may then be employed for the second precipitation step.

During the production of solid carbonate compositions from thebicarbonate rich product or component thereof (e.g., LCP), one mol ofCO₂ may be produced for every 2 mols of bicarbonate ion from thebicarbonate rich product or component thereof (e.g., LCP). For example,where solid carbonate compositions are produced by adding calcium cationto the bicarbonate rich product or component thereof (e.g., LCP), theproduction of solid carbonate compositions, e.g., the form of amorphouscalcium carbonate minerals, may proceed according to the followingreaction:

2HCO₃ ⁻+Ca⁺⁺↔CaCO₃.H₂O+CO₂

Ca⁺⁺ _((aq))+2HCO_(3(aq)) ⁻↔CaCO_(3(s))+H₂O_((l))+CO_(2(g))

While the above reaction shows the production of 1 mol of CO₂, 2 molesof CO₂ from the CO₂ containing gas were initially converted tobicarbonate. As such, the overall process sequesters a net 1 mol of CO₂in a carbonate compound and produces 1 mol of substantially pure CO2product gas, which may be sequestered by injection into a subsurfacegeological location, as described in greater detail below. Therefore,the process is an effective CO₂ sequestration process.

In producing the CO₂ sequestering material from a CO₂-containing gas, aCO₂-containing gas may be contacted with an aqueous medium underconditions sufficient to remove CO₂ from the CO₂-containing gas andproduce the bicarbonate component, e.g., as described above. While anyconvenient protocol may be employed, protocols of interest include, butare not limited to, those described in U.S. patent application Ser. No.14/112,495; the disclosure of which is herein incorporated by reference.

As reviewed above, contact of the bicarbonate rich product with thecation source results in production of a substantially pure CO₂ productgas. The phrase “substantially pure” means that the product gas is pureCO₂ or is a CO₂ containing gas that has a limited amount of other,non-CO₂ components.

Following production of the CO₂ product gas, aspects of the inventioninclude injecting the product CO₂ gas into a subsurface geologicallocation to sequester CO₂. By injecting is meant introducing or placingthe CO₂ product gas into a subsurface geological location. Subsurfacegeological locations may vary, and include both subterranean locationsand deep ocean locations. Subterranean locations of interest include avariety of different underground geological formations, such as fossilfuel reservoirs, e.g., oil fields, gas fields and un-mineable coalseams; saline reservoirs, such as saline formations and saline-filledbasalt formations; deep aquifers; porous geological formations such aspartially or fully depleted oil or gas formations, salt caverns, sulfurcaverns and sulfur domes; etc.

In some instances, the CO₂ product gas may be pressurized prior toinjection into the subsurface geological location. To accomplish suchpressurization the gaseous CO₂ can be compressed in one or more stageswith, where desired, after cooling and condensation of additional water.The modestly pressurized CO₂ can then be further dried, where desired,by conventional methods such as through the use of molecular sieves andpassed to a CO₂ condenser where the CO₂ is cooled and liquefied. The CO₂can then be efficiently pumped with minimum power to a pressurenecessary to deliver the CO₂ to a depth within the geological formationor the ocean depth at which CO₂ injection is desired. Alternatively, theCO₂ can be compressed through a series of stages and discharged as asuper critical fluid at a pressure matching that necessary for injectioninto the geological formation or deep ocean. Where desired, the CO₂ maybe transported, e.g., via pipeline, rail, truck or other suitableprotocol, from the production site to the subsurface geologicalformation.

In some instances, the CO₂ product gas is employed in an enhanced oilrecovery (EOR) protocol. Enhanced Oil Recovery (abbreviated EOR) is ageneric term for techniques for increasing the amount of crude oil thatcan be extracted from an oil field. Enhanced oil recovery is also calledimproved oil recovery or tertiary recovery. In EOR protocols, the CO₂product gas is injected into a subterranean oil deposit or reservoir.

As mentioned above, in addition to the CO₂ product gas, the methodsresult in the production of a carbonate composition. The productcarbonate compositions may vary greatly. The precipitated product mayinclude one or more different carbonate compounds, such as two or moredifferent carbonate compounds, e.g., three or more different carbonatecompounds, five or more different carbonate compounds, etc., includingnon-distinct, amorphous carbonate compounds. Carbonate compounds ofprecipitated products of the invention may be compounds having amolecular formulation X_(m)(CO₃)_(n) where X is any element orcombination of elements that can chemically bond with a carbonate groupor its multiple, wherein X is in certain embodiments an alkaline earthmetal and not an alkali metal; wherein m and n are stoichiometricpositive integers. These carbonate compounds may have a molecularformula of X_(m)(CO₃)_(n).H₂O, where there are one or more structuralwaters in the molecular formula. The amount of carbonate in the product,as determined by coulometry using the protocol described as coulometrictitration, may be 40% or higher, such as 70% or higher, including 80% orhigher.

The carbonate compounds of the precipitated products may include anumber of different cations, such as but not limited to ionic speciesof: calcium, magnesium, sodium, potassium, sulfur, boron, silicon,strontium, and combinations thereof. Of interest are carbonate compoundsof divalent metal cations, such as calcium and magnesium carbonatecompounds. Specific carbonate compounds of interest include, but are notlimited to: calcium carbonate minerals, magnesium carbonate minerals andcalcium magnesium carbonate minerals. Calcium carbonate minerals ofinterest include, but are not limited to: calcite (CaCO₃), aragonite(CaCO₃), vaterite (CaCO₃), ikaite (CaCO₃.6H₂O), and amorphous calciumcarbonate (CaCO₃). Magnesium carbonate minerals of interest include, butare not limited to magnesite (MgCO₃), barringtonite (MgCO₃.2H₂O),nesquehonite (MgCO₃.3H₂O), lanfordite (MgCO₃.5H₂O), hydromagnisite, andamorphous magnesium calcium carbonate (MgCO₃). Calcium magnesiumcarbonate minerals of interest include, but are not limited to dolomite(CaMg)(CO₃)₂), huntite (Mg₃Ca(CO₃)₄) and sergeevite(Ca₂Mg₁₁(CO₃)₁₃.H₂O). The carbonate compounds of the product may includeone or more waters of hydration, or may be anhydrous. In some instances,the amount by weight of magnesium carbonate compounds in the precipitateexceeds the amount by weight of calcium carbonate compounds in theprecipitate. For example, the amount by weight of magnesium carbonatecompounds in the precipitate may exceed the amount by weight calciumcarbonate compounds in the precipitate by 5% or more, such as 10% ormore, 15% or more, 20% or more, 25% or more, 30% or more. In someinstances, the weight ratio of magnesium carbonate compounds to calciumcarbonate compounds in the precipitate ranges from 1.5-5 to 1, such as2-4 to 1 including 2-3 to 1. In some instances, the precipitated productmay include hydroxides, such as divalent metal ion hydroxides, e.g.,calcium and/or magnesium hydroxides.

In some embodiments, one or more additional components or co-products(i.e., products produced from other starting non-CO₂ materials (e.g.,non-CO₂ pollutant material, e.g., SOx, NOx, etc.) under the sameconditions employed to convert CO₂ into carbonates and/or bicarbonates)are precipitated or trapped in precipitation material formed bycontacting the waste gas stream comprising these additional componentswith an aqueous solution comprising divalent cations (e.g., alkalineearth metal ions such as, but not limited to, Ca²⁺ and Mg²⁺. Inaddition, CaCO₃, MgCO₃, and related compounds may be formed withoutadditional release of CO₂. Sulfates, sulfites, and the like of calciumand/or magnesium may be precipitated or trapped in precipitationmaterial (further comprising, for example, calcium and/or magnesiumcarbonates) produced from waste gas streams comprising SOx (e.g., SO₂).Magnesium and calcium may react to form MgSO₄, CaSO₄, respectively, aswell as other magnesium-containing and calcium-containing compounds(e.g., sulfites), effectively removing sulfur from the flue gas streamwithout a desulfurization step such as flue gas desulfurization (“FGD”).In such embodiments of the invention, catalysts (e.g., carbonicanhydrase) may be employed where desired in the gas-liquid contactingstep to catalytically hydrate CO₂ in the presence of SOx, andoptionally, NOx and other criteria pollutants. In instances where theaqueous solution of divalent cations contains high levels of sulfurcompounds (e.g., sulfate), the aqueous solution may be enriched withcalcium and magnesium so that calcium and magnesium are available toform carbonate and/or bicarbonate compounds after, or in addition to,formation of CaSO₄, MgSO₄, and related compounds.

In some embodiments, a desulfurization step may be staged to coincidewith precipitation of carbonate- and/or bicarbonate-containingprecipitation material, or the desulfurization step may be staged tooccur before precipitation. In such embodiments of the invention,catalysts (e.g., carbonic anhydrase) may be used in gas-liquidcontacting step to catalytically hydrate CO₂ in the absence of SOx, orin the presence of very low levels of SOx. In some embodiments, multiplereaction products (e.g., MgCO₃, CaCO₃, CaSO₄, mixtures of the foregoing,and the like) are collected at different stages, while in otherembodiments a single reaction product (e.g., precipitation materialcomprising carbonates, bicarbonates, sulfates, etc.) is collected. Instep with these embodiments, other components, such as heavy metals(e.g., mercury, mercury salts, mercury-containing compounds), may betrapped in the carbonate- and/or bicarbonate-containing precipitationmaterial or may precipitate separately.

Precipitation of solid carbonate compositions from a dissolved inorganiccarbon (DIC) composition (e.g., an LCP composition as employed in abicarbonate-mediated sequestration protocol), such as described above,results in the production of a composition that includes bothprecipitated solid carbonate compositions, as well as the remainingliquid from which the precipitated product was produced (i.e., themother liquor). This composition may be present as a slurry of theprecipitate and mother liquor.

The carbonate precipitation conditions may vary, as desired. Forexample, the carbonate precipitation conditions may be transientamorphous calcium carbonate precipitation conditions. In some instances,the carbonate precipitation conditions produce a first precipitatedcarbonate composition and second precipitated carbonate composition. Insuch instances, the first precipitated carbonate composition may be anamorphous calcium carbonate (ACC) and the second precipitated carbonatecomposition is vaterite precursor ACC. In such embodiments, the methodfurther comprises separating the first and second precipitated carbonatecompositions from each other. Conveniently, the first and secondprecipitated carbonate compositions are separated from each other with amembrane. In some instances, the method further includes combining theseparated first and second precipitated carbonate compositions.

This product slurry may be disposed of in some manner following itsproduction. The phrase “disposed of” means that the slurry or a portionthereof, e.g., the solid carbonate composition portion thereof, iseither placed at a storage site or employed for a further use in anotherproduct, i.e., a manufactured or man-made item, where it is “stored” inthat other product at least for the expected lifetime of that otherproduct.

In some instances, this disposal step includes forwarding the slurrycomposition described above to a long-term storage site. The storagesite could be an above ground site, a below ground site or an underwatersite. In these embodiments, following placement of the slurry at thestorage site, the mother liquor component of the slurry may naturallyseparate from the precipitate, e.g., via evaporation, dispersal, etc.

Where desired, the resultant precipitated product (i.e., solid carbonatecomposition) may be separated from the resultant mother liquor.Separation of the solid carbonate composition can be achieved using anyconvenient approach. For example, separation may be achieved by dryingthe solid carbonate composition to produce a dried solid carbonatecomposition. Drying protocols of interest include filtering theprecipitate from the mother liquor to produce a filtrate and thenair-drying the filtrate. Where the filtrate is air dried, air-drying maybe at a temperature ranging from −70 to 120° C., as desired. In someinstances, drying may include placing the slurry at a drying site, suchas a tailings pond, and allowing the liquid component of the precipitateto evaporate and leave behind the desired dried product. Also ofinterest are freeze-drying (i.e., lyophilization) protocols, where thesolid carbonate composition is frozen, the surrounding pressure isreduced and enough heat is added to allow the frozen water in thematerial to sublime directly from the frozen precipitate phase to gas.Yet another drying protocol of interest is spray drying, where theliquid containing the precipitate is dried by feeding it through a hotgas, e.g., where the liquid feed is pumped through an atomizer into amain drying chamber and a hot gas is passed as a co-current orcounter-current to the atomizer direction.

Where the precipitated product is separated from the mother liquor, theresultant precipitate may be disposed of in a variety of different ways,as further elaborated below. For example, the precipitate may beemployed as a component of a building material, as reviewed in greaterdetail below. Alternatively, the precipitate may be placed at along-term storage site (sometimes referred to in the art as a carbonbank), where the site may be above ground site, a below ground site oran underwater, e.g., deepwater, site.

In certain embodiments, the product carbonate composition is refined(i.e., processed) in some manner prior to subsequent use. Refinement mayinclude a variety of different protocols. In certain embodiments, theproduct is subjected to mechanical refinement, e.g., grinding, in orderto obtain a product with desired physical properties, e.g., particlesize, etc. In certain embodiments, the precipitate is combined with ahydraulic cement, e.g., as a supplemental cementitious material, as asand, a gravel, as an aggregate, etc. In certain embodiments, one ormore components may be added to the precipitate, e.g., where theprecipitate is to be employed as a cement, e.g., one or more additives,sands, aggregates, supplemental cementitious materials, etc. to producefinal product, e.g., concrete or mortar.

In certain embodiments, the carbonate compound is utilized to produceaggregates, e.g., as described in U.S. Pat. No. 7,914,685, thedisclosure of which is herein incorporated by reference. In certainembodiments, the carbonate compound precipitate is employed as acomponent of hydraulic cement. The term “hydraulic cement” is employedin its conventional sense to refer to a composition that sets andhardens after combining with water. Setting and hardening of the productproduced by combination of the cements of the invention with an aqueousfluid result from the production of hydrates that are formed from thecement upon reaction with water, where the hydrates are essentiallyinsoluble in water. Such carbonate compound component hydraulic cements,methods for their manufacture and use include, but are not limited to,those described in U.S. Pat. No. 7,735,274; the disclosure of which isherein incorporated by reference.

Also of interest are dissolution precipitation cements like orthopediccalcium phosphate cements that undergo dissolution into solution andprecipitate out an alternate material. Dissolution precipitation cementsare that are not hydrating however will employ solution as an ion sinkwhich mediates the recrystallization of the lower energy state materialwhich is likened to concrete and can contain volume fillers such asaggregates and finer aggregates.

Also of interest are formed building materials. The formed buildingmaterials of the invention may vary greatly. By “formed” is meantshaped, e.g., molded, cast, cut or otherwise produced, into a man-madestructure defined physical shape, i.e., configuration. Formed buildingmaterials are distinct from amorphous building materials, e.g.,particulate (such as powder) compositions that do not have a defined andstable shape, but instead conform to the container in which they areheld, e.g., a bag or other container. Illustrative formed buildingmaterials include, but are not limited to: bricks; boards; conduits;beams; basins; columns; drywalls etc. Further examples and detailsregarding formed building materials include those described in UnitedStates Published Application No. US20110290156; the disclosure of whichis herein incorporated by reference.

Also of interest are non-cementitious manufactured items that includethe product of the invention as a component. Non-cementitiousmanufactured items of the invention may vary greatly. Bynon-cementitious is meant that the compositions are not hydrauliccements. As such, the compositions are not dried compositions that, whencombined with a setting fluid, such as water, set to produce a stableproduct. Illustrative compositions include, but are not limited to:paper products; polymeric products; lubricants; asphalt products;paints; personal care products, such as cosmetics, toothpastes,deodorants, soaps and shampoos; human ingestible products, includingboth liquids and solids; agricultural products, such as soil amendmentproducts and animal feeds; etc. Further examples and detailsnon-cementitious manufactured items include those described in U.S. Pat.No. 7,829,053; the disclosure of which is herein incorporated byreference.

In some instances, the solid carbonate product may be employed in albedoenhancing applications. Albedo, i.e., reflection coefficient, refers tothe diffuse reflectivity or reflecting power of a surface. It is definedas the ratio of reflected radiation from the surface to incidentradiation upon it. Albedo is a dimensionless fraction, and may beexpressed as a ratio or a percentage. Albedo is measured on a scale fromzero for no reflecting power of a perfectly black surface, to 1 forperfect reflection of a white surface. While albedo depends on thefrequency of the radiation, as used herein Albedo is given withoutreference to a particular wavelength and thus refers to an averageacross the spectrum of visible light, i.e., from about 380 to about 740nm.

As the methods of these embodiments are methods of enhancing albedo of asurface, the methods in some instances result in a magnitude of increasein albedo (as compared to a suitable control, e.g., the albedo of thesame surface not subjected to methods of invention) that is 0.05 orgreater, such as 0.1 or greater, e.g., 0.2 or greater, 0.3 or greater,0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 orgreater, 0.9 or greater, including 0.95 or greater, including up to 1.0.As such, aspects of the subject methods include increasing albedo of asurface to 0.1 or greater, such as 0.2 or greater, e.g., 0.3 or greater,0.4 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 orgreater, 0.9 or greater, 0.95 or greater, including 0.975 or greater andup to approximately 1.0.

Aspects of the methods include associating with a surface of interest anamount of a highly reflective microcrystalline or amorphous materialcomposition effective to enhance the albedo of the surface by a desiredamount, such as the amounts listed above. The material composition maybe associated with the target surface using any convenient protocol. Assuch, the material composition may be associated with the target surfaceby incorporating the material into the material of the object having thesurface to be modified. For example, where the target surface is thesurface of a building material, such as a roof tile or concrete mixture,the material composition may be included in the composition of thematerial so as to be present on the target surface of the object.Alternatively, the material composition may be positioned on at least aportion of the target surface, e.g., by coating the target surface withthe composition. Where the surface is coated with the materialcomposition, the thickness of the resultant coating on the surface mayvary, and in some instances may range from 0.1 mm to 25 mm, such as 2 mmto 20 mm and including 5 mm to 10 mm. Applications in use as highlyreflective pigments in paints and other coatings like photovoltaic solarpanels are also of interest.

The albedo of a variety of surfaces may be enhanced. Surfaces ofinterest include at least partially facing skyward surfaces of bothman-made and naturally occurring objects. Man-made surfaces of interestinclude, but are not limited to: roads, sidewalks, buildings andcomponents thereof, e.g., roofs and components thereof (roof shingles)and sides, runways, and other man-made structures, e.g., walls, dams,monuments, decorative objects, etc. Naturally occurring surfaces ofinterest include, but are not limited to: plant surfaces, e.g., as foundin both forested and non-forested areas, non-vegetated locations, water,e.g., lake, ocean and sea surfaces, etc.

Methods of using the carbonate precipitate compounds described herein invarying applications as described above, including albedo enhancingapplications, as well as compositions produced thereby, are furtherdescribed in U.S. application Ser. Nos. 14/112,495 and 14/214,129; thedisclosures of which applications are herein incorporated by reference.

In addition to (or instead of) processing CO₂ (e.g., by producing pureCO₂ and then sequestering it as described above), embodiments of theinvention also encompass processing other products resulting fromcombustion of carbon-based fuels. For example, at least a portion of oneor more of NOx, SOx, VOC, mercury and mercury-containing compounds, orparticulates that may be present in the CO₂-containing gas may be fixed(i.e., precipitated, trapped, etc.) in precipitation material. In suchembodiments, the methods may include using and/or disposing of suchproducts, e.g., in a manner sufficient to sequester such products andthe pollutants thereof, e.g., NOx, SOx, VOC, mercury andmercury-containing compounds, or particulates, in a manner analogous tothat described above for CO₂. Accordingly, embodiments of the inventioninclude methods of depleting an initial gas of one or more of suchpollutants, and then sequestering such pollutants.

As such, embodiments of the invention include methods of removingnon-CO2 pollutants, e.g., NOx, SOx, VOC, mercury and mercury-containingcompounds, or particulates, from a gas containing such pollutants. Inother words, methods of separating non-CO₂ pollutants from a gascontaining such pollutants are provided, where an input gas containingthe target non-CO₂ pollutant(s) is processed to produce an output gasthat has less of the target non-CO₂ pollutant(s) than the input gas. Theoutput gas of the methods described herein may be referred to as“non-CO₂ pollutant depleted gas.” The amount of non-CO₂ pollutant(s) inthe treated gas is less than the amount of non-CO₂ pollutant(s) that ispresent in the input gas, where in some instances the amount of non-CO₂pollutant(s) in the depleted gas is 95% or less, e.g., 90% or less, 85%or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% orless, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less,30% or less, 25% or less, 20% or less, 15% or less, 10% or less, 5% orless, than the amount of target pollutant(s) that is present in theinput containing gas.

Systems

Aspects of the invention further include systems, e.g., small scaledevices, processing plants or factories, for sequestering CO₂, e.g., bypracticing methods as described above. Systems of the invention may haveany configuration that enables practice of the particular sequestrationmethod of interest. In some embodiments, systems of the inventioninclude: a source of the CO₂ containing gas; a source of an aqueousmedium; a reactor configured to contact the CO₂ containing gas with theaqueous medium under conditions sufficient to produce a bicarbonate richproduct, as well as a solid carbonate composition and a product CO₂ gasfrom the bicarbonate rich product; and an injector configured to injectthe product CO₂ gas in a subsurface geological location.

Any convenient bicarbonate buffered aqueous medium source may beincluded in the system. In certain embodiments, the source includes astructure having an input for aqueous medium, such as a pipe or conduitfrom an ocean, etc. Where the aqueous medium is seawater, the source maybe an input that is in fluid communication with the sea water, e.g.,such as where the input is a pipe line or feed from ocean water to aland based system or an inlet port in the hull of ship, e.g., where thesystem is part of a ship, e.g., in an ocean based system.

The CO₂ containing gas source may vary. Examples of CO₂ containing gassources include, but are not limited to, pipes, ducts, or conduits whichdirect the CO₂ containing gas to a portion of the system, e.g., to areactor configured to produce a bicarbonate rich product, e.g., thatincludes LCPs. The aqueous medium source and the CO₂ containing gassource are connected to a reactor configured to contact the CO₂containing gas with the bicarbonate buffered aqueous medium underconditions sufficient to produce a bicarbonate rich product, such asdescribed above. The reactor may include any of a number of components,such as temperature regulators (e.g., configured to heat the water to adesired temperature), chemical additive components, e.g., forintroducing agents that enhance bicarbonate production, mechanicalagitation and physical stirring mechanisms. The reactor may include acatalyst that mediates the conversion of CO₂ to bicarbonate, such asdescribed above. The reactor may also include components that allow forthe monitoring of one or more parameters such as internal reactorpressure, pH, metal-ion concentration, and pCO₂.

The reactor further includes an output conveyance for the bicarbonaterich product. In some embodiments, the output conveyance may beconfigured to transport the bicarbonate rich component to a storagesite, such as an injection into subsurface brine reservoirs, a tailingspond for disposal or in a naturally occurring body of water, e.g.,ocean, sea, lake, or river. In yet other embodiments, the output maytransfer the bicarbonate rich product to a packaging station, e.g., forputting into containers and packaging with a hydraulic cement.Alternatively, the output may convey the bicarbonate rich product tosecond reactor, which may be configured to produce solid carbonatecompositions, i.e., precipitates, from the bicarbonate rich product.

In some instances, the systems include a second reactor configured tofurther process the bicarbonate rich product, e.g., to dry the product,to combine the product with one or more additional components, e.g., acement additive, to produce solid carbonate compositions from abicarbonate rich product, etc. For embodiments where the reactor isconfigured to produce a carbonate product, such reactors include aninput for the bicarbonate rich product, as well as an input for a sourceof cations (such as described above) which introduces the cations intothe bicarbonate rich product in a manner sufficient to causeprecipitation of solid carbonate compounds. Where desired, this reactormay be operably coupled to a separator configured to separate aprecipitated carbonate mineral composition from a mother liquor, whichare produced from the bicarbonate rich product in the reactor. Incertain embodiments, the separator may achieve separation of aprecipitated carbonate mineral composition from a mother liquor by amechanical approach, e.g., where bulk excess water is drained from theprecipitate by gravity or with the addition of a vacuum, mechanicalpressing, filtering the precipitate from the mother liquor to produce afiltrate, centrifugation or by gravitational sedimentation of theprecipitate and drainage of the mother liquor. The system may alsoinclude a washing station where bulk dewatered precipitate from theseparator is washed, e.g., to remove salts and other solutes from theprecipitate, prior to drying at the drying station. In some instances,the system further includes a drying station for drying the precipitatedcarbonate mineral composition produced by the carbonate mineralprecipitation station. Depending on the particular drying protocol ofthe system, the drying station may include a filtration element, freezedrying structure, spray drying structure, etc. as described more fullyabove. The system may include a conveyer, e.g., duct, from theindustrial plant that is connected to the dryer so that a gaseous wastestream (i.e., industrial plant flue gas) may be contacted directly withthe wet precipitate in the drying stage. The resultant dried precipitatemay undergo further processing, e.g., grinding, milling, in refiningstation, in order to obtain desired physical properties. One or morecomponents may be added to the precipitate where the precipitate is usedas a building material.

The system may further outlet conveyers, e.g., conveyer belt, slurrypump, that allow for the removal of precipitate from one or more of thefollowing: the reactor, drying station, washing station or from therefining station. The product of the precipitation reaction may bedisposed of in a number of different ways. The precipitate may betransported to a long term storage site in empty conveyance vehicles,e.g., barges, train cars, trucks, etc., that may include both aboveground and underground storage facilities. In other embodiments, theprecipitate may be disposed of in an underwater location. Any convenientprotocol for transporting the composition to the site of disposal may beemployed. In certain embodiments, a pipeline or analogous slurryconveyance structure may be employed, where these approaches may includeactive pumping, gravitational mediated flow, etc.

In certain embodiments, the system will further include a station forpreparing a building material, such as cement, from the precipitate.This station can be configured to produce a variety of cements,aggregates, or cementitious materials from the precipitate, e.g., asdescribed in U.S. Pat. No. 7,735,274; the disclosure of whichapplication is herein incorporated by reference.

In addition, the system includes an output for the substantially pureproduct CO₂ gas. The output may be operatively coupled to an injectorconfigured to inject the product CO₂ into a subsurface geologicallocation, e.g., as described above. Where desired, the system mayinclude a compressor and/or temperature modulator for the CO₂ productgas, where such component, when present, are operatively positionedbetween the output and the injector. As the injector and output areoperatively coupled, they may be directly connected to each other orconnected via a conveyor, such as a pipeline.

Systems of the invention may be configured as continuous or batchsystems, as desired. Additional details regarding reactors of interestmay be found in U.S. patent application Ser. No. 14/112,495; thedisclosure of which is herein incorporated by reference.

The following examples are offered by way of illustration and not by wayof limitation.

EXPERIMENTAL I. Materials and Methods A. NTA Image Collection

Data was collected on a NS-500 nanoparticle tracking analyzer (Malvern)due to its capabilities to analyze dilute species in solution in a waythat dynamic light scattering cannot (V. Filipe, A. Hawe, W. Jiskoot,Critical Evaluation of Nanoparticle Tracking Analysis (NTA) by NanoSightfor the Measurement of Nanoparticles and Protein Aggregates.Pharmaceutical Research 27, 796 (2010)). Raw data consisted of 60 secondrecordings of the scattering projections of various solution sat acamera length setting of 16. Still shots used in figures arerepresentative still shots of this recording. The recording wasprocessed to generate the histogram of particle size vs. particle countwith a bin size of 20 nm. The settings used to process the raw data werea detection threshold of 6, auto-blur, auto-minimum expected particlesize, and a solution viscosity equal to that of water at 25° C. (0.89cP).

B. Sample Preparations for NTA Image Collection

The simulated Cretaceous seawater at a pCO₂ simulating the cretaceousera seen in FIG. 1, panel A was created by mixing 23.9 g NaCl(Sigma-Aldrich, S9888), 4.01 g Na₂SO₄, anhydrous (Acros Organics, S421),0.68 g KCl (Sigma Aldrich, P9541), 0.2 g NaHCO₃, (Aqua Solutions,144-55-8), 3 g MgCl₂ hexahydrate (Research Products International Corp.,M24000), and 3.5 g CaCl₂ dihydrate (Aqua Solutions, C0630) into 1 literof nanopure water to create a simulated Cretaceous era seawater (1:1[Mg²⁺]/[Ca²⁺] ratio). The solution was titrated to pH 8.1 with NaOH (aq)(Alfa Aesar, A 18395) and then gassed with CO₂ to pH 7.7 to simulate thehigher P_(CO2) of the Cretaceous era. The value, pH 7.7 was chosen byusing Geochemist's Workbench™ to estimate the pH of the saltwatersolution in equilibrium with a P_(CO2) of 7 times that of the modern eraprior to the industrial revolution (210 ppm). Modern seawater (seen inFIG. 1, panel B) was obtained from Monterey Bay, Calif. and wassand-filtered at the Monterey Bay Aquarium Institute at Moss Landing,Calif. The simple bicarbonate solution seen in FIG. 1, panel C consistedof 100 mM NaHCO₃ and 100 mM NaCl. The control with which it was comparedin FIG. 6 consisted of a 200 mM NaCl solution. Adult Fetal Bovine serumwas analyzed by using Adult Bovine Serum (Sigma B9433, batch 12B519) anddiluting 1:100 in nanopure water prior to filtering with a 200 nmdiameter pore size syringe filter (Whatman Cat. No. 6809-1122).

C. Sample Preparation NMR Measurements

A solution containing 100 mM NaHCO₃ and 100 mM NaCl was created using100% ¹³C substituted NaHCO₃ (Cambridge Isotopes, 372382). No chemicalshift standard was added to the solution to ensure electrolyte behavioris naturally occurring. All NMR data was obtained using a Varian Inova500 magnet operating at 126 MHz using a 5 mm broadband probe. Allexperiments were conducted at 298 Kelvin. Deuterium oxide (Aldrich,151882) was used to obtain a lock at a volume fraction of 2.5% of thetotal sample. Data was processed using NUTS™ and Microsoft Excelsoftware when deconvolution of overlapping spectral peaks was required.90° pulses were used with acquisition times of 6.35 seconds. The T₂relaxation measurements were conducted using aCarr-Purcell-Meibloom-Gill (CPMG) sequence with increasing tau (τ) timesof 0.025, 0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4 seconds.

D. Refractive Index Measurement

Species in the size range of the bicarbonate-rich LCP are generally inthe Rayleigh scattering regime, where a close approximation of theefficiency of light scattering is given by equation (S1) below:

$\begin{matrix}{{I \propto \sigma_{s}} = {\frac{2\pi^{5}}{3}\frac{d^{6}}{\lambda^{4}}\left( \frac{n^{2} - 1}{n^{2} + 2} \right)^{2}}} & ({S1})\end{matrix}$

Where:

-   -   I is the measured intensity of the scattering event    -   σ_(s) is the scattering cross section    -   d is the species diameter    -   λ is the wavelength of incident light, here λ=402 nm    -   n is the ratio of the scattering species refractive index to the        solvent refractive index

Equation (S1) relates the measured intensity of a scattering event (I)to the diameter of the scattering center species (d), the wavelength ofincident light (λ) and the refractive indices (RI) of the scatteringspecies and solvent. The NTA technique measures/directly and d by meansof Brownian motion. If the RI of the solvent is known, a standard with aknown RI can be used to calibrate the technique to account for softwareand equipment measurements of the relative intensity. Equation (S1) canthen be used to calculate the RI for the scattering species (C.Gardiner, Y. J. Ferreira, R. A. Dragovic, C. W. G. Redman, I. L.Sargent, Extracellular vesicle sizing and enumeration by nanoparticletracking analysis. Journal of Extracellular Vesicles 2, 19671 (2013); E.van der Pol et al., in International Society for Extracellular Vesicles2014. (Rotterdam, Netherlands, 2014)).

To determine the RI of bicarbonate-rich LCP, silica (SiO₂) nanoparticlesof 50, 80, 100 nm (hydrated diameters of 62, 92, 116 nm, respectively)were used as the standard reference material (RI=1.51). Equal masses ofthe different sized SiO₂ nanoparticles were placed into a solution of100 mM Na₂CO₃ to the concentration of approximately 10⁸ particles/mL.The standard solution was then titrated with 1 N HCl, to pH 9.0, andanalyzed for light scattering events using NTA. FIG. 7 displays thestandard curve. This standard curve was applied to the data shown inFIG. 2C to demonstrate the reliability of the technique and to verifyand validate the technique.

E. Pitzer Modeling

We carried out thermodynamic calculations of ion activities in carbonatesolutions using Geochemist's Workbench software (GWB). The plot in FIG.11 was obtained by subtracting the ion activity predicted by Pizer'sEquations from the ion activity predicted by Debye-Hückel (D-H) theory.D-H theory accurately predicts ion activities up to about 10 mMolalconcentration. Our assumption is that non-ideality at higherconcentrations may be in part due to formation of LCP which removes someions from bulk solution and thus lowers their activities. The sum of thedeviations from D-H activities shown in FIG. 11 are simply the sum ofthe deviations for all ions and approximate the percent of ions presentas LCP (assuming it is responsible for the lowered ion activities). Wethen compare trends in ion activities vs. pH for our calculated percentof ions present in LCP with observations of the volume of LCP based onlight scattering measurements of real carbonate solutions.

F. Concentration of Bicarbonate-Rich LCP by Membrane Processes

Twenty gallons of solution of LCP droplets was concentrated with a DK(GE Osmonics) NF membrane and contained dissolved ions of sodium (Na⁺),potassium (K⁺), chloride (Cl⁻) and bicarbonate (HCO₃ ⁻);conductivity=10.8 mS. The NF system houses two custom made 1.8×12 inchelements, purchased from Membrane Development Specialists (Solana Beach,Calif.), and is operated by a positive displacement pump capable ofmoving roughly 2 gal water per minute. The NF system was operated at theflow rate specified by the membrane manufacturer. The feed solution wasconcentrated by continuously recirculating the concentrate back into thefeed and removing permeate in incremental volumes. Potassium chloride(Sigma Aldrich) and sodium bicarbonate (Aqua Solutions, Sigma Aldrich,Church & Dwight Co. Inc.) were purchased commercially and were usedwithout further purification.

Rejection of NaHCO₃ by various membrane types—reverse osmosis (RO), X20(TriSep); nanofiltration (NF), DK (GE Osmonics); ultrafiltration (UF),MPF-36 (Koch Membrane Systems)—were investigated with a custom madeflat-plate casing that houses 4-inch diameter sample elements, purchasedfrom Membrane Development Specialists (Solana Beach, Calif.). Theflat-plate system uses a positive displacement pump to move roughly 2gal water per minute. Here, back-pressure on the system is adjusted sothat permeate flow rate—in gallons of permeate per square foot ofmembrane per day (GFD)—meet the manufacturers specification. The IonRejection was calculated by dividing the conductivity of the permeate bythe conductivity of the feed solution. Sodium bicarbonate (AquaSolutions, Sigma Aldrich, Church & Dwight Co. Inc.) was purchasedcommercially and was used without further purification.

G. Preparation of Mortar Specimens

The mortar cube specimens were mixed according to ASTM C109/C109M (ASTMStandard C109/C109M, Standard Test Method for Compressive Strength ofHydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens). (ASTMInternational, West Conshohocken, Pa., 2013)) and used variations of thefollowing components: Ottowa silica sand (ELE International), 16-200mesh glass grade limestone sand (Blue Mountain Mineral, Colombia,Calif.), Basalite Type II-V cement, 15% interground (IG) cement, water,and liquid condensed phase (LCP) liquid. The 15% interground cement wasprepared by blending 325 μm-sized natural limestone (Blue MountainMinerals, Columbia, Calif.) with the Basalite cement and was then milledfor 16 hours (PTA-02 Ball Mill with 10 L Jar). Mortar components wereblended in a Hobart Mixer (Hobart Inc., Troy Ohio) according to ASTMC305 (ASTM Standard C305, Standard Practice for Mechanical Mixing ofHydraulic Cement Pastes and Mortars of Plastic Consistency. (ASTMInternational, West Conshohocken, Pa., 2013)). Mortar was transferred to50 mm×50 mm cubic brass molds, specified by ASTM C109/C109M. Samples setin 100% relative humidity (RH), 73° F., were demolded at 1 day andfurther stored at 100% RH, 73° F., until mechanically loaded. Sampleswere mechanically loaded at 200 lb/s on an ELE load frame (Accu-TekTouch 250 Series) in accordance with ASTM C109/C109M.

H. FTIR Analyses and Sample Preparation

FTIR spectra were recorded using a Nicolet IS-10 by Thermo-Fisher with aHeNe laser and a fast recovery deuterated triglycerine sulfate (DTGS)detector. Scans were collected on a Germanium ATR crystal at resolutionof 16 and at optical velocity of 0.4747. FTIR samples were prepared byadding 0.25 M CaCl₂ (Sigma, Lot#BCBL2738 & Deionized Water) to 0.5MNaHCO₃ (Aqua Solutions, Lot #319302 & Deionized Water) (FIG. 8). 20 μlwas pipetted onto the ATR crystal and the reaction was recorded in atime resolved fashion using a Macro applied to Omnic 9.2 software. Thespectra were recorded at 0, 10, 20, and 1800 seconds.

I. Dissolved Inorganic Carbon (DIC) Analysis

The dissolved inorganic carbon (DIC) content of solution and solidcarbonate samples were determined by acidometric titration andcoulometric detection using a CM150 carbon analysis system (UIC, Inc.).The samples were typically titrated with 2N H₂PO₄ (Sigma Aldrich). Todetect CO₂ evolved in reactions of CaCl₂ (Sigma Aldrich) with NaHCO₃(Aqua Solutions), however, the samples were not titrated with H₂PO₄, butrather, a solution of CaCl₂ was titrated with a solution of NaHCO₃because titration with H₂PO₄ would result in liberation of CO₂ fromCaCO₃. This allowed CO₂ to be quantified by coulometric detection; anysolid formed in the reaction was then isolated, dried and analyzed byFTIR to confirm its composition as CaCO₃. All analyses using the CM150system were completed at 40° C.

J. Time-Resolved pH Measurement

The pH was recorded in a time resolved manner using an OrionStar A215 pHmeter with an Orion 8157BNUMD Ross Ultra pH/ATC Probe. Data was loggedusing StarCom 1.0 sampling every 3 seconds while dosing 0.25 M CaCl₂solution (Sigma, Lot#BCBL2738 & Deionized Water) into 0.5 M NaHCO₃solution (Aqua Solutions, Lot#319302 & Deionized Water) and 0.5 M Na₂CO₃(Sigma Lot#SLBD98664)(FIG. 8, panel G and FIG. 8, panel H)

K. Synthesis of Calcium Carbonates Materials with Desirable Properties

Carbonate was produced by mixing CaCl₂ (aq) and NaHCO₃ (aq) at a molarratio of 1:2, similar to what is described in the Timer-resolved pHmeasurement section of the Material and Methods. The precipitate wasthen pressurized using a carver press to 20,000 lbf and allowed it todwell for 30 minutes. The compact calcium carbonate was then placed in ahumidity chamber (Fisher Scientific Isotemp Oven Model 615F, made 100%humid with water) for 7 days at 40° C. Finally, the sample was cured for12 days in 1 M Na₂CO₃ solution, which was kept in a water bath tomaintain the temperature at 40° C.

L. Solar Reflectance Measurements and Calculations

Solar reflectance spectra were collected using Perkin-Elmer Lambda 950UV-Vis-NIR spectrometer loaded with 150 mm Integrating Sphere. The datawere recorded with 5 nm interval using UV Winlab 6.0.2 software. Thesolar reflectance was calculated based on clear sky Air Mass 1 GlobalHorizontal (AM1GH) (R. Levinson, H. Akbari, P. Berdahl, Measuring solarreflectance—Part I: Defining a metric that accurately predicts solarheat gain. Solar Energy 84, 1717 (2010); R. Levinson, H. Akbari, P.Berdahl, Measuring solar reflectance—Part II: Review of practicalmethods. Solar Energy 84, 1745 (2010)) and ASTM Standard E892-87terrestrial solar irradiance (ASTM Standard E892-87 for TerrestrialSolar Spectral Irradiance at Air Mass 1.5 for a 37-Deg tilted surface.(ASTM International, West Conshohocken, Pa., 1992)) to compute solar(averaged over range 300-2500 nm), UV (averaged over range 300-400 nm),visible (averaged over range 400-700 nm), and near-infrared (averagedover range 700-2500 nm) reflectance.

M. Life Cycle Analysis

Calculations of lb CO₂/yd³ mortar were based on the assumption that anaverage of 2,044 lb of CO₂ is emitted for every 2,205 lb of OrdinaryPortland Cement (OPC) produced in the U.S., depending on fuel type, rawingredients, and the energy efficiency of the cement plant (NationalReady-Mix Concrete Association, Concrete CO2 Fact Sheet, based on themost recent survey of Portland Cement Association members. (February2012)) (essentially 1:1 CO₂:OPC produced). Therefore ASTM C109/C109Mmortar cube mix design has 1,057 lb CO₂/yd³ mortar (extrapolated frommix design detailed in FIG. 4, panel B); this also assumes no CO₂contributions from the water and aggregate components of the mix design.When a carbon-reducing LCP liquid that contains 1 wt % CO₂ is used as acomplete water replacement in the Ordinary mix design, the lb CO₂/yd³mortar is reduced by 5 lb CO₂. When the carbon-reducing liquid is usedin combination with a 15% replacement of OPC by interground (IG)limestone, the lb CO₂/yd³ mortar is reduced to 898 lb CO₂/yd³ (from 1057lb CO₂/yd³). This is due to the 1 wt % CO₂ in the liquid and the 15%offset of CO₂ that would have otherwise come from the manufacturing ofOPC.

II. Discussion

Here, we report the discovery of acidic bicarbonate-rich LCP in severalnatural solutions like seawater, and suggest that it may be used as aCO₂ sink in carbon sequestration. We provide evidence that thebicarbonate-rich LCP does not require supersaturated conditions withrespect to any solid divalent inorganic carbonate and is neither mineralspecific nor transient, but rather, is a fundamental electrolytebehavior exhibited by bicarbonate (HCO₃ ⁻) ions. The resulting potentialfor additional control over the bicarbonate-rich LCP droplets allow fora previously unknown means to manipulate solvated inorganic carbonchemistry, such as mechanical separation and concentration in thesolution state, and the production of synthetic minerals with superiorproperties. This discovery has far-reaching ramifications in such fieldsas oceanography, environmental sciences, material sciences andlarge-scale anthropogenic carbon dioxide separation and sequestrationvia carbonate mineralization.

We report here droplets of an apparent LCP in a variety of solutions bymeans of a light scattering technique: nanoparticle tracking analysis(NTA). We analyzed both synthesized inorganic solutions and naturalionic solution also containing organic moieties including, a synthesizedinorganic Cretaceous Period seawater composition (FIG. 1, panel A),modern seawater (FIG. 1, panel B), synthesized simple, undersaturatedsolutions containing monovalent inorganic sodium bicarbonate and sodiumchloride (NaHCO₃/NaCl), an no divalent cations (FIG. 1, panel C) andsolutions of bovine fetal calf serum (FIG. 1, panel D), to demonstratethe ubiquitous nature of the LCP that may exist in a variety ofcompositions which participate in, and affect chemistry. Note that thenatural solutions, modern seawater and serum containing organic moieties(right hand panels B and D) show an abundance of droplets compared tothe pure synthesized inorganic solutions (left hand panels A and C).

The LCP droplets range from 0 to 400 nm, with a size distribution andoverall count that appears to be environment specific. When divalentions, particularly Ca²⁺, are present in the solutions, even atnear-neutral pH, the HCO₃ ⁻ is particularly concentrated in thehyperalkaline LCP phase. This observation may explain the nucleationmechanism that leads to much higher nucleation rates than might betheoretically expected, as well as calcium carbonate polymorphspecificity in a way that the absence of such condensation mechanisms donot (P. G. Vekilov, Crystal Growth & Design 10, 5007 (December, 2010)).An example, in FIG. 6, demonstrates how the NTA technique was used tomeasure the effects of Mg²⁺:Ca²⁺ ratio on the amount of LCP droplets ina sodium bicarbonate solution. The behavior of LCP appears to parallelthe prevalence of aragonite vs. calcite precipitation. This isconsistent with the observation that biomineralization associated withprolific marine calcifying taxa flourished in the Cretaceous Period,when atmospheric carbon dioxide levels were significantly higher and theocean would have been hyperalkaline as a result (S. M. Stanley, ChemicalReviews 108, 4483 (2008 Nov. 12, 2008)).

What is particularly fascinating is that bicarbonate-rich LCP forms inthe simple, highly undersaturated solution of 100 mM NaHCO₃ and 100 mMNaCl shown in FIG. 1, panel C. In contrast to previous studies, thissuggests that the condensation is due to a fundamental bicarbonate ionpropensity to condense, and not to strong interactions with divalentions in supersaturated states, with respect to mineral formation. Thedroplets do not form in bicarbonate-deficient solutions of similar ionicstrength such as in 200 mM NaCl (see FIG. 7, panel B), indicating thatbicarbonate rich LCP is a fundamental electrolyte behavior that is notspecific to a particular biomineral or to a solid nucleation pathway. Astable, acidic, long-lived bicarbonate-rich LCP may serve as aconcentrated carbon sink and provide a fundamental chemical mechanism,through manipulation with additives, in which CO₂ over a wide range ofconcentrations could be converted to hyperalkaline droplets of LCP richin bicarbonate ions and concentrated and manipulated for carbonsequestration processes via carbonate mineralization.

Nuclear magnetic resonance (NMR) spectroscopy has been used in the pastto characterize bicarbonate-rich LCPs (M. A. Bewernitz, D. Gebauer, J.Long, H. Coelfen, L. B. Gower, Faraday Discussions 159, 291 (2012)) andearly HCO₃/CO₃ ²⁻ nucleation behavior (D. Gebauer et al., AngewandteChemie International Edition 49, 8889 (2010)). The same NaHCO₃/NaClsolution analyzed in FIG. 1C was characterized using 1D transverserelaxation measurements in order to identify and analyze the LCP, (seeFIGS. 2, panel A and 2, panel B, respectively). The 1D ¹³C NMR spectrumin FIG. 2, panel A shows a doublet that is consistent with the presenceof two similar, yet non-identical solution states coexisting inequilibrium, e.g., LCP and mother solution. Deconvolution of the twopeaks suggests that, over the course of the six-second time average usedto acquire the data, approximately 30% of the inorganic carbon insolution has participated in LCP. This is consistent with a long-lastingseparate phase, with different chemistry that is not rapidly transientin a way to average out over several seconds. The CPMG T₂ relaxationmeasurement in FIG. 2, panel B demonstrates that the two phases havedifferent T₂ relaxation times, re-enforcing the notion that the twopeaks are due to HCO₃ ⁻ residing in two distinct solution environments.The apparent bicarbonate-rich LCP phase has a shorter T₂ relaxation thanthe mother solution suggesting that it is more viscous and/or moreconcentrated than the mother solution. The results from NMR experimentssupport the NTA data and again demonstrate the presence of a LCP in theabsence of divalent cations, in solutions that are undersaturated withrespect to any solid phases, e.g., NaHCO₃. The data support the thesisthat LCPs are not a specific step in the nucleation process, but rathera ubiquitous and fundamental electrolyte behavior occurring in solutionscontaining HCO₃ ⁻.

Because NTA has proven a successful and novel method of providingestimated refractive indices (RI) of unknowns in earlier studies(Bewernitz et al., Id.; V. Filipe, A. Hawe, W. Jiskoot, Pharm. Res. 27,796 (2010)), light scattering measurements by NTA were used here tocalculate a first-order approximation of the RI of bicarbonate-rich LCPdroplets. The results are shown in FIG. 2. In a 100 mM NaHCO₃/NaClsolution, the bicarbonate-rich LCP droplets show a low intensity,polydisperse size distribution. This suggests that the droplets have alarger RI than the mother solution and that their RI is a range ratherthan a single value. FIG. 2, panel C shows a fit to a group ofstatistically relevant data points, given their increased certaintyindicated by larger data points, giving a calculated RI of 1.355 for theLCP droplets. To encompass the range of the apparent diverse values ofRI for bicarbonate-rich LCP, a lower-limit fit, inclusive of all the LCPdroplets, gives a RI of 1.347. It must be stressed that the RI valuesattributed to LCP are consistent with saltwater indices and not withsolid NaCl, NaHCO₃, or Na₂CO₃; all of which are massively undersaturatedin the solution. Salinity of the bicarbonate-rich LCP was estimated byplotting saltwater RI vs. salinity obtained from previous work (X. Quan,E. S. Fry, Applied Optics 34, 3477 (1995)), and is shown in FIG. 2,panel D. The values are consistent with a bicarbonate-rich LCP, havingsalinity between 20 and 60 g/L as compared to the mother solution withsalinity of 15 g/L. In other words, the bicarbonate-rich LCP has asalinity of four times greater (or more) compared to the mothersolution. This is consistent with a previous report that described LCPas a condensed solution state of bicarbonate and to the best of ourknowledge, represents the first attempt to estimate the salinity ofbicarbonate-rich LCP droplets using a novel technique.

Since the resulting bicarbonate-rich LCP droplets act like intact largermoieties rather than individual ions, they can be mechanically separatedand recovered from their bulk solution (see FIG. 3). Nanofiltration (NF)is an established water softening membrane technology that has proven tobe especially effective at concentrating bicarbonate-rich LCP. AlthoughLCP can be concentrated with tighter reverse osmosis (RO) membraneelements as well, NF elements require much less mechanical load and canachieve similar levels of LCP rejection as is obtained by RO. Todemonstrate, an aqueous solution of 50 mM sodium bicarbonate/potassiumchloride (NaHCO₃/KCl) containing bicarbonate-rich LCP was concentratedusing membrane filtration with various membranes with different poresizes. The results are shown in FIG. 3.

FIG. 3, panel A shows that as the NaHCO₃/KCl solution is concentratedwith a NF element (pore size diameter <2 nm), the overall dissolvedinorganic carbon (DIC=bicarbonate in FIG. 3, panel A) increases, as doesthe amount of bicarbonate-rich LCP droplets (NTA images, FIG. 3, panelB). The rejection (concentration) properties of NaHCO₃ in FIG. 3, panelC and FIG. 3, panel D suggest that the bicarbonate-rich LCP droplets arelarger, on average, than 10 nm due to their rejection by the NF and RO,but not by ultrafiltration. This observation is consistent with the sizedistribution measured by NTA in FIG. 1, panel C as being several dozennm in diameter. The NF technology appears to be a new approach toaqueous HCO₃ ⁻ chemistry, by means of mechanics to separate andmanipulate the solution. The above data points to the bicarbonate-richLCP as a mechanism for sequestering CO₂ into a capture solution andconcentrating it, i.e., the NF process is one that would allow forconcentration of bicarbonate-rich LCP droplets in carbon capturesolutions derived from flue gas. LCP being bicarbonate-rich suggeststhat, with the addition of Ca²⁺, solid nucleation of CaCO₃ may proceedthrough a biomimetic bicarbonate pathway. This is similar to theproposed mineralization process used by calcifying aquatic invertebratesthat form mineralized skeletons, shown in equation (1), where CO₂ isconverted to solid carbonate material via the reaction of Ca²⁺ with twoequivalents of HCO₃ ⁻ (ΔG=−27.3 kJ mol⁻¹).

CaCl₂(aq)+2NaHCO₃(aq)=CaCO3(s)+CO₂(aq)+H₂O(l)+2NaCl(aq)  (1)

CaCO₃ formation appears to follow this pathway when it is occurring insolutions containing significant amounts of bicarbonate-rich LCP. Forresults supporting the formation of CaCO₃ through equation (1) at pH'sranging from 6 to 8.5 and achieving yields approaching 90% for bothCaCO₃ and CO₂, see FIG. 8 in the Supplemental Materials. Additionally,ATR studies supporting this behavior in real time are shown in FIG. 8.

The reaction in equation (1) occurs at near-neutral pH and has broadenabling implications for large-scale CO₂ sequestration and productionof synthetic inorganic carbonate solids as compared to the traditionalapproach, seen in equation (2), which involves reacting Ca²⁺ with CO₃²⁻, equation (2) (ΔG=−49.87 kJ mol⁻¹).

CaCl₂(aq)+Na₂CO₃(aq)=CaCO₃(s)+2NaCl(aq)  (2)

The necessity of maintaining a high pH of the system to mineralizethrough equation (2) is a major limitation due to the prohibitiveexpense of producing/supplying large amounts of high pH alkalinity.Mineralization through equation (1) reduces the energy/expense due tothe requirement to maintain a pH neutral environment that favors thebicarbonate ion (pH 6.5-8.5). The drawback is that the reaction inequation (1) produces an equivalent of pure stream CO₂ for everyequivalent of CaCO₃ produced. This may prove desirable, however, in thepursuit of geological subsurface sequestration. Currently the primarysolution for managing carbon emissions on a world-wide sustainablebasis, geologic sequestration requires that CO₂ be in a substantiallypure form, however, as it must be compressed and liquefied for transportand injection into subsurface geological reservoirs, which requiressubsequent monitoring. The most significant quantities of carbonemissions originate from Portland cement plants, coal- and naturalgas-fired power plants, all of which emit dilute streams of CO₂, butcontain mainly nitrogen. Current state-of-the-art technologies to purifyCO₂ from industrial flue gas, e.g., amine scrubbing (G. T. Rochelle,Science 325, 1652 (2009)), are energy intensive primarily due to thestripping of pure CO₂ out of the capture solution. At a coal-fired powerplant, for example, purifying the CO₂ from a flue stream can requiremore than 35% of the electricity generated by the plant. In the contextof mineralizing CaCO₃ through the reaction in equation (1), however,where two equivalents of CO₂ (as HCO₃ ⁻) produce one equivalent of pureCO₂ and one equivalent of sequestered CO₂ (as CaCO₃ for buildingmaterials), such energy intensive loads might be circumvented.

Ideally, the synthetic CaCO₃ produced in the process will be used in thebuilt environment as limestone aggregate for concrete, asphalt and roadbase. A formulation of water, cement and aggregate constituents,concrete is the most used building material in the world and representsthe largest potential sustainable reservoir for CO₂ sequestration. Thecarbon footprint of a cubic yard (yd³) of concrete, however, islarge—averaging ¾ ton of CO2 per ton of cement—and is largely due to theenergy intensive process of manufacturing ordinary Portland cement (OPC)(National Ready-Mix Concrete Association, Concrete CO2 Fact Sheet, basedon the most recent survey of Portland Cement Association members. Anaverage of 2,044 lb of CO2 is emitted for every 2,205 lb of ordinaryPortland cement (OPC) produced in the U.S., depending on fuel type, rawingredients and the energy efficiency of the cement plant, (2012)). Itis of significant interest to replace traditional components of concretewith novel, carbon-reducing components. When used in formulations whereOPC is replaced by, e.g., natural limestone, or preferably, syntheticlimestone derived from an emission source, and bicarbonate-rich LCPsolutions are incorporated, the new formulation has a significant impacton the carbon footprint per yd³ concrete (see FIG. 4B). This includesthe offset of CO₂ that would have otherwise come from the manufacturingof OPC, as well as storage of CO₂ sequestered in the concrete. We haveverified that carbon-reducing components can be substituted into mortarformulations with increased performance. FIG. 4, panel A shows thetime-dependent compressive strength data for a series of mortarspecimens. One mortar formulation that substituted natural limestone forOPC, cured faster than the ordinary mortar formulation. The limestone,similar to the synthetic CaCO₃ product in equation (1), was interground(IG) with the OPC to maximize reactive surface area. In a seconditeration, ordinary mix water of the mortar formulation was completelyreplaced by concentrated bicarbonate-rich LCP solution, and lead to evenfaster curing times. The carbon footprint of the mortar specimens thatused carbon-reducing components is reduced significantly compared to theordinary mortar formulation (FIG. 4, panel C).

In addition to being valuable in concrete formulations, the carbonateminerals produced from LCP solutions via the reaction in equation (1)exhibit unusually high solar reflectance (SR) relative to knowncommercial and natural materials (FIG. 4, panel D). High SR is desirablefor commercial cool roofing technologies as a means to mitigate heatisland effects in urban areas (H. Akbari, S. Menon, A. Rosenfeld,Climatic Change 95, 275 (2009); M. Santamouris, A. Synnefa, T. Karlessi,Solar Energy 85, 3085 (2011)), reducing the convective and radiativethermal gain of a surface and significantly reducing energy consumptionand costs associated with cooling structures. Calcium carbonate materialprecipitated via the reaction in equation (1) displays superior albedoproperties, having high solar reflectance across the entire solarspectrum, a property with significant implications with regard to energyefficiency in cool materials. The synthetic CaCO₃ even outperforms TiO₂,the current standard for albedo against which materials are rated.

Electrolyte solutions deviate from ideal behaviors due to a decrease inthe activity of individual ions. Many such mechanisms are suspected tocontribute, at least in part, to the loss of activity. These includeDebye-Hückel screening, ion-pairing, and the recently discoveredprenucleation clustering (PNC) (D. Gebauer, A. Volkel, H. Coelfen,Science 322, 1819 (2008)). LCP is an additional phenomenon that canaccount for a portion, or even the majority of, the non-ideality ofconcentrated salt solutions, simply by altering ion activity due to theincorporation of ions into an LCP phase. The ions present in a separateLCP phase do not contribute to thermodynamic measurements of the “mothersolution” leading to a lowering the activities of those species and achange in the mother solution equilibrium (see FIG. 9). This may lead tomis-interpretations regarding the state of the global system if thetwo-phase system is not considered. In other words, the activity of aspecific ion or solvated species may drop, not because its coefficientchanged, but because it actually left the system to another phase.Explicit accounting for LCP will simplify our thermodynamic and kineticmodels of electrolyte solutions and provide new insights into previouslyunexplained behaviors. For additional data and experiments thatcorrelate the LCP to non-ideal behavior, see FIGS. 10 and 11.

In light of these findings, we show an approach to modeling saltsolution properties by considering the formation of a two-phase LCPsystem. This would be beneficial to all fields which study electrolytebehaviors but particularly in the field of oceanography. It is currentlyassumed that carbon in the ocean is comprised of a single phase inequilibrium with Earth's atmosphere and that by knowing any twovariables (P_(CO2), pH, dissolved inorganic carbon (DIC) and alkalinity,for a given temperature, salinity and pressure), all the other systemparameters can be calculated. This does not hold true for a multiphasesystem. Recent studies of calcium carbonate (CaCO₃) solubility andformation suggest that fundamental electrolyte behaviors, such as PNC'sand LCP (D. Gebauer, H. Coelfen, Nano Today 6, 564 (2011)) affectcarbonate chemistry. Assumptions surrounding the negative effect ofadditional atmospheric CO₂ leading to ocean acidification (R. E. Zeebe,Annual Review of Earth and Planetary Sciences 40, 141 (2012); B. Honischet al., Science 335, 1058 (Mar. 2, 2012, 2012)) may need to bere-evaluated. The effect may not be strickly the reduction of thesolubility of CaCO3 but may affect the bicarbonate pathway toward CaCO₃(J. B. Ries, A. L. Cohen, D. C. McCorkle, Geology 37, 1131 (Dec. 1,2009, 2009)). It may be more accurate to refer to the process as oceanalkalinization (increase in bicarbonate) rather than oceanacidification. This may explain the explosion of biogenic CaCO₃formation that occurred during the Cretaceous Period when atmosphericP_(CO2) was much larger than it is today. The partial pressure of CO₂(P_(CO2)) in Earth's atmosphere has varied considerably over PhanerozoicPeriod. Oceanic HCO₃ ⁻ concentration and alkalinity of the ocean wouldhave increased with increasing P_(CO2) leading to higherbicarbonate-rich LCP and more biomineral formation through that pathway.This is consistent with recent studies (C. P. Jury, R. F. Whitehead, A.M. Szmant, Global Change Biology 16, 1632 (2010); M. D.Iglesias-Rodriguez et al., Science 320, 336 (Apr. 18, 2008, 2008)). Inlight of the LCP discovery in the ocean, these seemingly disparate linesof evidence from modern oceanography and the geologic record, correlatewith regard to optimal conditions for CaCO₃ formation from bicarbonatesolutions.

Having demonstrated the potential to store sequestered CO₂ in LCP,concentrate LCP, and use the concentrated solution to precipitatematerials with superior properties, we show that the findings presentedhere may be utilized in an approach to carbon capture and sequestrationas a four-stage process (see process flow diagram in FIG. 13). Carboncapture solutions are created using a membrane-derived alkali recoveryprocess driven by ion concentration gradients such as the ones readilyavailable as cooling waters for power plants or waste from desalinationplants. This capture solution is combined with a CO₂ emission source ina gas-liquid contactor to form HCO₃ solutions containing hyperalkaline,bicarbonate-rich LCP droplets. At inland locations, geologic brines insedimentary basins available as produced waters contain a Mg²⁺:Ca²⁺ratio more similar to Cretaceous Period seawater compositions thanmodern seawater. Combination of concentrated bicarbonate-rich LCP withhard Ca²⁺ brine solution via the reaction in equation (1) results in theformation of synthetic CaCO₃ for use as, e.g., building materialsdescribed above, and the concomitant evolution of pure CO₂, for use ingeological subsurface sequestration. If, for example, the process werefitted to a 500 MW coal-fired power plant, 9,410 tons per day (TPD) ofsolid CaCO₃ mineral and 4,138 TPD pure CO₂ would be produced, assuming52% recovery of CO₂ (see FIG. 13 for detailed metrics at each stage ofthe process). The energy consumption lies mainly in pumping the waterrequired for the process.

The approach described in this report is comprehensive in that it (i)captures and permanently sequesters CO₂ from emission point sources,producing large scale commodity material in the form of inorganiccarbonates for the built environment, an approach that provides a carbonsink large enough to manage the CO₂ problem and (ii) produces purestream CO₂ for efficient subsurface geological storage. Many studiesremain to further understand and characterize the novel bicarbonate-richLCP. Given the recent change in U.S. policy mandating reduced carbonemissions, we felt that reporting the existence and potential carbonsequestration implications of bicarbonate-rich LCP to the scientificcommunity will stimulate further work studying the carbon sequestrationpotential of LCP across all scientific disciplines in a way that mayhelp promote full compliance with the new carbon mandates.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the teachings of this invention that certain changes andmodifications may be made thereto without departing from the spirit orscope of the appended claims.

Accordingly, the preceding merely illustrates the principles of theinvention. It will be appreciated that those skilled in the art will beable to devise various arrangements which, although not explicitlydescribed or shown herein, embody the principles of the invention andare included within its spirit and scope. Furthermore, all examples andconditional language recited herein are principally intended to aid thereader in understanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

1-27. (canceled)
 28. A system for sequestering CO₂, the systemcomprising: a source of the CO₂ containing gas; a source of an aqueousmedium; a reactor configured to: contact the CO₂ containing gas with theaqueous medium under conditions sufficient to produce a bicarbonate richproduct; and produce a solid carbonate composition and a product CO2 gasfrom the bicarbonate rich product; and an injector configured to injectthe product CO₂ gas in a subsurface geological location.
 29. A method ofremoving a non-CO₂ pollutant from a multicomponent gaseous stream, themethod comprising: contacting the multi-component gaseous stream with anaqueous medium under conditions sufficient to produce a bicarbonate richproduct; and subjecting the bicarbonate rich product to carbonateprecipitation conditions to remove a non-CO₂ pollutant from themulticomponent gaseous stream.
 30. The method according to claim 29,wherein the non-CO2 pollutant is selected from the group consisting ofNOx, SOx, VOC, heavy metals, particulate matter, and combinationsthereof.
 31. The system according to claim 28, wherein the aqueousmedium is a bicarbonate buffered aqueous medium.
 32. The systemaccording to claim 31, wherein the bicarbonate buffered aqueous mediumhas a pH ranging from 8 to
 10. 33. The system according to claim 28,wherein the CO₂ containing gaseous stream is a multicomponent gaseousstream.
 34. The system according to claim 28, wherein the bicarbonaterich product comprises droplets of a liquid condensed phase (LCP) in abulk liquid.
 35. The system according to claim 28, wherein the CO₂containing gas is contacted with the aqueous medium in the presence of acatalyst that mediates the conversion of CO₂ to bicarbonate.
 36. Thesystem according to claim 28, wherein the solid carbonate composition isproduced without the use of an alkalinity source.
 37. The systemaccording to claim 28, wherein the product CO₂ gas comprisessubstantially pure CO₂.
 38. The system according to claim 28, furthercomprising compressing the product CO₂ gas prior to injecting theproduct CO₂ gas in the subsurface geological location.
 39. The systemaccording to claim 28, wherein the subsurface geological location is asubterranean location.
 40. The system according to claim 28, wherein thesystem is configured to produce a commodity from the solid carbonatecomposition.
 41. The system according to claim 40, wherein the commodityis a building material.
 42. The system according to claim 41, whereinthe building material is an aggregate.
 43. The system according to claim42, wherein the building material is a cement or supplementalcementitious material.
 44. The system according to claim 28, wherein themethod produces a mole of purified CO₂ for every two moles of CO₂removed from the gaseous stream.
 45. The system according to claim 28,wherein the CO₂ containing gas is obtained from an industrial plant. 46.The system according to claim 45, wherein the CO₂ containing gas is aflue gas.